Large area group III nitride crystals and substrates, methods of making, and methods of use

ABSTRACT

Embodiments of the present disclosure include techniques related to techniques for processing materials for manufacture of group-III metal nitride and gallium based substrates. More specifically, embodiments of the disclosure include techniques for growing large area substrates using a combination of processing techniques. Merely by way of example, the disclosure can be applied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic and electronic devices, lasers, light emitting diodes, solar cells, photo electrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, and others.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 16/882,219, filed May 22, 2020, which claims thebenefit of U.S. Provisional Application No. 62/975,078, filed Feb. 11,2020. This application also claims the benefit of U.S. ProvisionalApplication No. 63/006,700, filed Apr. 7, 2020. Each of these patentapplications are incorporated by reference herein.

BACKGROUND Field

This disclosure relates generally to techniques for processing materialsfor manufacture of gallium-containing nitride substrates and utilizationof these substrates in optoelectronic and electronic devices. Morespecifically, embodiments of the disclosure include techniques forgrowing large area crystals and substrates using a combination ofprocessing techniques.

Description of the Related Art

Gallium nitride (GaN) based optoelectronic and electronic devices are oftremendous commercial importance. The quality and reliability of thesedevices, however, is compromised by high defect levels, particularlythreading dislocations, grain boundaries, and strain in semiconductorlayers of the devices. Threading dislocations can arise from latticemismatch of GaN based semiconductor layers to a non-GaN substrate suchas sapphire or silicon carbide. Grain boundaries can arise from thecoalescence fronts of epitaxially-overgrown layers. Additional defectscan arise from thermal expansion mismatch, impurities, and tiltboundaries, depending on the details of the growth of the layers.

The presence of defects has deleterious effects on epitaxially-grownlayers. Such effects include compromising electronic device performance.To overcome these defects, techniques have been proposed that requirecomplex, tedious fabrication processes to reduce the concentrationand/or impact of the defects. While a substantial number of conventionalgrowth methods for gallium nitride crystals have been proposed,limitations still exist. That is, conventional methods still meritimprovement to be cost effective and efficient.

Progress has been made in the growth of large-area gallium nitridecrystals with considerably lower defect levels than heteroepitaxial GaNlayers. However, most techniques for growth of large-area GaN substratesinvolve GaN deposition on a non-GaN substrate, such as sapphire or GaAs.This approach generally gives rise to threading dislocations at averageconcentrations of 10⁵-10⁷ cm⁻² over the surface of thick boules, as wellas significant bow, stress, and strain. Reduced concentrations ofthreading dislocations are desirable for a number of applications. Bow,stress, and strain can cause low yields when slicing the boules intowafers, make the wafers susceptible to cracking during down-streamprocessing, and may also negatively impact device reliability andlifetime. Another consequence of the bow, stress, and strain is that,during growth in m-plane and semipolar directions, even bynear-equilibrium techniques such as ammonothermal growth, significantconcentrations of stacking faults may be generated. In addition, thequality of c-plane growth may be unsatisfactory, due to formation ofcracks, multiple crystallographic domains, and the like. Capability tomanufacture substrates larger than 2 inches is currently very limited,as is capability to produce large-area GaN substrates with a nonpolar orsemipolar crystallographic orientation. Most large area substrates aremanufactured by vapor-phase methods, such as hydride vapor phase epitaxy(HVPE), which are relatively expensive. A less-expensive method isdesired, while also achieving large area and low threading dislocationdensities as quickly as possible.

Ammonothermal crystal growth has a number of advantages over HVPE as ameans for manufacturing GaN boules. However, the performance ofammonothermal GaN crystal growth processing may be significantlydependent on the size and quality of seed crystals. Seed crystalsfabricated by HVPE may suffer from many of the limitations describedabove, and large area ammonothermally-grown crystals are not widelyavailable.

Legacy techniques have suggested methods for merging elementary GaN seedcrystals into a larger compound crystal by a tiling method. Some of thelegacy methods use elementary GaN seed crystals grown by hydride vaporphase epitaxy (HVPE) and involve polishing the edges of the elementarycrystals at oblique angles to cause merger in fast-growing directions.Many or most of the legacy methods use HVPE as the crystal growth methodto merge the seed crystals. Such legacy techniques, however, havelimitations. Typically, for example, legacy techniques do not specifythe accuracy of the crystallographic orientation, both polar andazimuthal, between the merged elementary seed crystals or provide amethod capable of producing highly accurate crystallographic registrybetween the elementary seed crystals and minimizing defects resultingfrom the merging of the elementary seed crystals. Ammonothermal GaNtypically has lattice constants that differ, at least slightly, fromthose of HVPE GaN. The presence of even a small mismatch in latticeconstants can cause stress and cracking in crystals grownammonothermally on HVPE seed crystals, particularly when tiling andcoalescence are involved. Further, cracking may occur during subsequentsawing or polishing of an ammonothermally-grown crystal formed on one ormore HVPE seed crystals.

Due to at least the issues described above, there is a need forsubstrates that have a lower defect density and are formed by techniquesthat improve the crystal growth process. Also, from the above, it isseen that techniques for improving crystal growth are highly desirable.

SUMMARY

Embodiments of the present disclosure include a free-standing group IIImetal nitride crystal. The free-standing crystal comprises a wurtzitecrystal structure, a first surface having a maximum dimension greaterthan 40 millimeters in a first direction, an average concentration ofstacking faults below 10³ cm⁻¹; an average concentration of threadingdislocations between 10¹ cm⁻² and 10⁶ cm⁻², wherein the averageconcentration of threading dislocations on the first surface variesperiodically by at least a factor of two in the first direction, theperiod of the variation in the first direction being between 5micrometers and 20 millimeters, and a miscut angle that varies by 0.1degree or less in the central 80% of the first surface of the crystalalong the first direction and by 0.1 degree or less in the central 80%of the first surface of the crystal along a second direction orthogonalto the first direction. The first surface comprises a plurality of firstregions, each of the plurality of first regions having alocally-approximately-linear array of threading dislocations with aconcentration between 5 cm⁻¹ and 10⁵ cm⁻¹, the first surface furthercomprises a plurality of second regions, each of the plurality of secondregions being disposed between an adjacent pair of the plurality offirst regions and having a concentration of threading dislocations below10⁵ cm⁻² and a concentration of stacking faults below 10³ cm⁻¹, and thefirst surface further comprises a plurality of third regions, each ofthe plurality of third regions being disposed within one of theplurality of second regions or between an adjacent pair of second andhaving a minimum dimension between 10 micrometers and 500 micrometersand threading dislocations with a concentration between 10³ cm⁻² and 10⁸cm⁻².

Embodiments of the present disclosure include a free-standing group IIImetal nitride crystal comprising at least two domains. Each of the atleast two domains include a group III metal selected from gallium,aluminum, and indium, or combinations thereof, and nitrogen. Each of theat least two domains has a wurtzite crystal structure and comprises afirst surface having a maximum dimension greater than 10 millimeters ina first direction, an average concentration of threading dislocationsbetween 10¹ cm⁻² and 1×10⁶ cm⁻², an average concentration of stackingfaults below 10³ cm⁻¹, a symmetric x-ray rocking curve full width athalf maximum less than 200 arcsec, an impurity concentration of Hgreater than 10¹⁷ cm⁻³, and an impurity concentration of at least one ofLi, Na, K, F, Cl, Br, and I greater than 10¹⁵ cm⁻³, as quantified bycalibrated secondary ion mass spectrometry. A concentration of thethreading dislocations within a first surface of a domain on the firstsurface can vary periodically by at least a factor of two in the firstdirection, a period of a variation in the first direction being between5 micrometers and 5 millimeters. The first surface comprises a pluralityof first regions, each of the plurality of first regions having alocally-approximately-linear array of threading dislocations with aconcentration between 5 cm⁻¹ and 10⁵ cm⁻¹. The first surface may furthercomprise a plurality of second regions, each of the plurality of secondregions being disposed between an adjacent pair of the plurality offirst regions and having a concentration of threading dislocations below10⁵ cm⁻² and a concentration of stacking faults below 10³ cm⁻¹. Thefirst surface may further comprise a plurality of third regions, each ofthe plurality of third regions being disposed within one of theplurality of second regions or between an adjacent pair of secondregions and having a minimum dimension between 10 micrometers and 500micrometers and threading dislocations with a concentration between 10¹cm⁻² and 10⁶ cm⁻². The free-standing group III metal nitride crystal hasa maximum dimension in the first direction greater than 40 millimeters,a crystallographic miscut varies by 0.2 degree or less in two orthogonaldirections over a central 80% of the crystal along the first directionand by 0.1 degree or less in two orthogonal directions over the central80% of the crystal along a second direction orthogonal to the firstdirection, and the at least two domains are separated by a line ofdislocations with a linear density between about 50 cm⁻¹ and about 5×10⁵cm⁻¹, and a polar misorientation angle γ between a first domain and asecond domain is greater than about 0.005 degrees and less than about0.2 degrees and misorientation angles α and β are greater than about0.01 degrees and less than about 1 degree.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising performing a bulkcrystal growth process on a tiled array of at least two seed crystals ina crystal growth apparatus, wherein the bulk crystal growth processcauses a bulk crystal layer grown from a first surface of a first seedcrystal and a bulk crystal layer grown from a first surface of a secondseed crystal to merge to form a compound crystal, a polar misorientationangle γ between a crystallographic orientation of the first surface ofthe first seed crystal and a crystallographic orientation of the firstsurface of the second seed crystal being greater than about 0.005degrees and less than about 0.2 degrees and azimuthal misorientationangles α and β between the crystallographic orientations of the firstsurfaces of the first and second seed crystals being greater than about0.01 degrees and less than about 1 degree, and each of the seed crystalscomprising at least one of gallium, aluminum, and indium and nitrogenand having a wurtzite crystal structure and a maximum dimension of atleast 5 millimeters. In some embodiments, the bulk crystal growthprocess is performed at a first temperature, the tiled array of at leasttwo seed crystals are positioned on a first surface of a mechanicalfixture during the bulk crystal growth process, the mechanical fixturecomprises at least a backing plate member and a clamp member, each ofwhich has a coefficient of thermal expansion that lies between 80% and99% of the coefficient of thermal expansion of the at least two seedcrystals averaged over a range between room temperature and the firsttemperature, and the coefficient of thermal expansion is measured in aplane parallel to the first surface.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising placing at leasttwo seed crystals each having a first surface on a mechanical fixture,placing the mechanical fixture into a crystal growth apparatus, andperforming a bulk crystal growth process at a second temperature,causing the first seed crystal and the second seed crystal to merge intoa compound crystal, wherein each of the seed crystals comprises at leastone of gallium, aluminum, and indium and nitrogen and has a wurtzitecrystal structure and a maximum dimension of at least 5 millimeters. Themechanical fixture comprises at least a backing plate member and a clampmember, each of which has a coefficient of thermal expansion that liesbetween 80% and 99% of the coefficient of thermal expansion of the atleast two seed crystals in a plane of the first surface, averaged over arange between room temperature and a second temperature, and a polarmisorientation angle γ between a crystallographic orientation of thefirst surface of a first seed crystal and a crystallographic orientationof the first surface of a second seed crystal is greater than about0.005 degrees and less than about 0.2 degrees and azimuthalmisorientation angles α and β between the crystallographic orientationsof the first surfaces of the first and second seed crystals are greaterthan about 0.01 degrees and less than about 1 degree.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising growing apolycrystalline group III metal nitride on a tiled array of at least twoseed crystals, wherein the tiled array of at least two seed crystalscomprises a first seed crystal that has a first surface and a secondsurface, and a second seed crystal that has a first surface and a secondsurface, and the process of growing a polycrystalline group III metalnitride on the tiled array of at least two seed crystals causes apolycrystalline group III metal nitride layer grown from the secondsurfaces of the first seed crystal and the second seed crystal to mergeto form a tiled assembly; and performing a bulk crystal growth processon the tiled assembly in a crystal growth apparatus. The bulk crystalgrowth process causes a bulk crystal layer grown over the first surfaceof the first seed crystal and a bulk crystal layer grown over the firstsurface of the second seed crystal to merge to form a compound crystal,a polar misorientation angle γ between a crystallographic orientation ofthe first surface of the first seed crystal and a crystallographicorientation of the first surface of the second seed crystal beinggreater than about 0.005 degrees and less than about 0.2 degrees andazimuthal misorientation angles α and β between the crystallographicorientations of the first surfaces of the first and second seed crystalsbeing greater than about 0.01 degrees and less than about 1 degree, andeach of the seed crystals comprises at least one of gallium, aluminum,and indium and nitrogen and has a wurtzite crystal structure and amaximum dimension of at least 5 millimeters.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising growing apolycrystalline group III metal nitride on a tiled array of at least twoseed crystals, separating the tiled assembly from a susceptor; andperforming a bulk crystal growth process on the tiled assembly in acrystal growth apparatus. The tiled array of at least two seed crystalscomprises a first seed crystal that has a first surface and a secondsurface; and a second seed crystal that has a first surface and a secondsurface, the tiled array of at least two seed crystals is disposed onthe susceptor, the process of growing a polycrystalline group III metalnitride on the tiled array of at least two seed crystals causes apolycrystalline group III metal nitride layer deposited on the secondsurfaces of the first seed crystal and the second seed crystal to mergeto form a tiled assembly. The bulk crystal growth process causes a bulkcrystal layer grown over the first surface of the first seed crystal anda bulk crystal layer grown over the first surface of the second seedcrystal to merge to form a compound crystal. A polar misorientationangle γ between a crystallographic orientation of the first surface ofthe first seed crystal and a crystallographic orientation of the firstsurface of the second seed crystal is greater than about 0.005 degreesand less than about 0.2 degrees and azimuthal misorientation angles αand β between the crystallographic orientations of the first surfaces ofthe first and second seed crystals are greater than about 0.01 degreesand less than about 1 degree, and each of the seed crystals comprises atleast one of gallium, aluminum, and indium and nitrogen and has awurtzite crystal structure and a maximum dimension of at least 5millimeters.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising placing at leasttwo seed crystals each having a first surface and a second surfaceopposite the first surface on a susceptor, placing the susceptor withina growth reactor and growing a polycrystalline group III metal nitrideover the second surfaces of the at least two seed crystals to form atiled assembly, separating the tiled assembly from the susceptor, andplacing the tiled assembly into a crystal growth apparatus, andperforming a bulk crystal growth process, causing the first seed crystaland the second seed crystal to merge into a compound crystal, whereineach of the seed crystals comprises at least one of gallium, aluminum,and indium and nitrogen and has a wurtzite crystal structure and amaximum dimension of at least 5 millimeters. Each of the seed crystalscomprises at least one of gallium, aluminum, and indium and nitrogen andhas a wurtzite crystal structure and a maximum dimension of at least 5millimeters. A polar misorientation angle γ between a crystallographicorientation of the first surface of a first seed crystal and acrystallographic orientation of the first surface of a second seedcrystal is greater than about 0.005 degrees and less than about 0.2degrees and azimuthal misorientation angles α and β between thecrystallographic orientations of the first surfaces of the first andsecond seed crystals are greater than about 0.01 degrees and less thanabout 1 degree.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising growing a group IIImetal nitride crystal layer over an array of at least two first seedcrystals, wherein each of the first seed crystals in the array of atleast two first seed crystals are aligned in an array that extends in afirst direction, and the process of growing the group III metal nitridecrystal layer forms a first tiled crystal, slicing the first tiledcrystal along a second direction orthogonal to the first direction,wherein slicing the first tiled crystal forms at least two second seedcrystals, and the at least two second seed crystals have a firstsurface, and growing a group III metal nitride crystal layer over anarray of at least two second seed crystals, wherein each of the secondseed crystals in the array of at least two second seed crystals arealigned in an array that extends in the first direction, and the processof growing the group III metal nitride crystal layer over the array ofthe at least two second seed crystals forms a second tiled crystal. Themethod further comprising slicing the second tiled crystal along boththe second direction and the first direction to form at least two thirdseed crystals, and growing a group III metal nitride crystal layer overan array of at least two third seed crystals, wherein each of the thirdseed crystals in the array of at least two third seed crystals arealigned in an array that extends in the first direction, and the processof growing the group III metal nitride crystal layer over the array ofthe at least two second seed crystals forms a third tiled crystal.

Embodiments of the present disclosure include a method for forming acompound group III metal nitride crystal, comprising placing at leasttwo first seed crystals each having a first surface and a second surfaceopposite the first surface on a support structure along a firstdirection, performing a first bulk crystal growth operation to coalescethe at least two first seed crystals to form a firstone-dimensional-tiled crystal, slicing the first one-dimensional-tiledcrystal along a second direction orthogonal to the first direction intoat least two second seed crystals, placing the at least two second seedcrystals having a first surface and a second surface opposite the firstsurface on a support structure along a third direction orthogonal to thefirst direction and to the second direction, performing a second bulkcrystal growth operation to coalesce the at least two second seedcrystals to form a second one-dimensional-tiled crystal, slicing thesecond one-dimensional-tiled crystal along both the second direction andthe first direction to form at least two third seed crystals, placingthe at least two third seed crystals having a first surface and a secondsurface opposite the first surface on a support structure along thefirst direction, performing a third bulk crystal growth operation tocoalesce the at least two third seed crystals to form a thirdone-dimensional-tiled crystal having a first surface and a secondsurface opposite the first surface and at least two domains. Each of theat least two domains within a third one-dimensional-tiled crystalencloses at least a portion of the at two third seed crystals. A polarmisorientation angle γ between a crystallographic orientation of thefirst surface of a first domain of the third one-dimensional-tiledcrystal and a crystallographic orientation of the first surface of asecond domain of the third one-dimensional-tiled crystal is greater thanabout 0.005 degrees and less than about 0.2 degrees and azimuthalmisorientation angles α and β between the crystallographic orientationsof the first surfaces of the first and second seed crystals are greaterthan about 0.01 degrees and less than about 1 degree. Each of the firstseed crystals, the second seed crystals, and the third seed crystalscomprise at least one of gallium, aluminum, and indium and nitrogen, hasa wurtzite crystal structure. Each of the first seed crystals, thesecond seed crystals, and the third seed crystals comprise a maximumdimension of at least 5 millimeters, and the crystallographicorientations of the first surfaces of each of the first seed crystals,the second seed crystals, and the third seed crystals are identical, towithin about 1 degree.

Embodiments of the present disclosure include a free-standing group IIImetal nitride substrate comprising at least two crystals, each of the atleast two crystals comprising a group III metal selected from gallium,aluminum, and indium, or combinations thereof, and nitrogen. Each of theat least two crystals having a wurtzite crystal structure comprises afirst surface having a maximum dimension greater than 10 millimeters ina first direction and a maximum dimension greater than 4 millimeters ina second direction orthogonal to the first direction, an averageconcentration of threading dislocations between 10¹ cm⁻² and 1×10⁶ cm⁻²,an average concentration of stacking faults below 10³ cm⁻¹, a symmetricx-ray rocking curve full width at half maximum less than 200 arcsec. Thefree-standing group III metal nitride substrate has a maximum dimensionin the first direction greater than 40 millimeters. The magnitude of acrystallographic miscut of the first surfaces of each of the at leasttwo crystals is equal, to within 0.5 degree, and the directions ofcrystallographic miscuts of the first surfaces of each of the at leasttwo crystals is equal, to within 10 degrees. Each of the at least twocrystals is bonded to a matrix member comprising polycrystalline GaN,and a polar misorientation angle γ between a first domain and a seconddomain is greater than about 0.005 degrees and less than about 0.2degrees and misorientation angles α and β are greater than about 0.01degrees and less than about 1 degree.

Embodiments of the present disclosure include a method for fabricating afree-standing group III metal nitride substrate comprising at least twodomains, the method comprising depositing a layer of polycrystalline GaNon an array of at least two seed crystals disposed on a susceptor toform a tiled composite member, and separating the tiled composite memberfrom the susceptor. The layer of polycrystalline GaN is formed a secondsurface, opposite to a first surface, of each of the at least two seedcrystals. Each of the at least two seed crystals comprise a group IIImetal selected from gallium, aluminum, and indium, or combinationsthereof, and nitrogen, and the at least two seed crystals having awurtzite crystal structure comprise a first surface having a maximumdimension greater than 10 millimeters in a first direction and a maximumdimension greater than 4 millimeters in a second direction orthogonal tothe first direction, an average concentration of threading dislocationsless than about 2×10⁷ cm⁻², an average concentration of stacking faultsbelow 10³ cm⁻¹, and a symmetric x-ray rocking curve full width at halfmaximum less than 200 arcsec.

Embodiments of the present disclosure include a method for fabricating afree-standing group III metal nitride substrate comprising at least twodomains, the method comprising providing at least two seed crystals,each of the at least two seed crystals comprising a group III metalselected from gallium, aluminum, and indium, or combinations thereof,and nitrogen, placing the at least two seed crystals on a susceptor,depositing a layer of polycrystalline GaN on a second surface, oppositethe first surface, of each of the at least two seed crystals to form atiled composite member, and removing the tiled composite member from thesusceptor. The at least two seed crystals having a wurtzite crystalstructure comprise a first surface having a maximum dimension greaterthan 10 millimeters in a first direction and a maximum dimension greaterthan 4 millimeters in a second direction orthogonal to the firstdirection, an average concentration of threading dislocations less thanabout 2×10⁷ cm⁻², an average concentration of stacking faults below 10³cm⁻¹, and a symmetric x-ray rocking curve full width at half maximumless than 200 arcsec. A polar misorientation angle γ between the firstsurface of a first seed crystal and the first surface of a second seedcrystal is greater than about 0.005 degrees and less than about 0.2degrees and misorientation angles α and pare greater than about 0.01degrees and less than about 1 degree.

Embodiments of the present disclosure include a free-standing group IIImetal nitride substrate, comprising an array of seed crystals, whereineach of the seed crystals in the array of seed crystals, comprise agroup III metal selected from gallium, aluminum, and indium, orcombinations thereof, and nitrogen, and a polycrystalline GaN layer thatis disposed over at least one surface of each of the seed crystalswithin the array of seed crystals. Each of the seed crystals having awurtzite crystal structure comprises a first surface having an averageconcentration of threading dislocations between 10¹ cm⁻² and 1×10⁶ cm⁻²,and an average concentration of stacking faults below 10³ cm⁻¹. Themagnitude of a crystallographic miscut of the first surfaces of each ofthe seed crystals is equal, to within 0.5 degree, and the directions ofcrystallographic miscuts of the first surfaces of each of the seedcrystals is equal, to within 10 degrees. A polar misorientation angle γbetween a first seed crystal of the array of seed crystals and a secondseed crystal of the array of seed crystals is greater than about 0.005degrees and less than about 0.2 degrees and misorientation angles α andβ are greater than about 0.01 degrees and less than about 1 degree.

Embodiments of the present disclosure include a free-standing group IIImetal nitride crystal, comprising a wurtzite crystal structure, at leasttwo domains, each of the at least two domains comprising a group IIImetal selected from gallium, aluminum, and indium, or combinationsthereof, and nitrogen; a first surface having a maximum dimensiongreater than 40 millimeters in a first direction, the first surfacecomprising a domain surface of each of the at least two domains, whereinthe domain surface of each of the at least two domains has a dimensionof at least 10 millimeters in the first direction, an averageconcentration of stacking faults below 10³ cm⁻¹, and an averageconcentration of threading dislocations between 10¹ cm⁻² and 10⁶ cm⁻².The average concentration of threading dislocations on the domainsurface of each of the at least two domains varies periodically by atleast a factor of two in the first direction, the period of thevariation in the first direction being between 5 micrometers and 20millimeters. The domain surface of each of the at least two domainscomprises a plurality of first regions, each of the plurality of firstregions having a locally-approximately-linear array of threadingdislocations with a concentration between 5 cm⁻¹ and 10⁵ cm⁻¹. Thedomain surface of each of the at least two domains further comprises aplurality of second regions, each of the plurality of second regionsbeing disposed between an adjacent pair of the plurality of firstregions and having a concentration of threading dislocations below 10⁵cm⁻² and a concentration of stacking faults below 10³ cm⁻¹. The domainsurface of each of the at least two domains further comprises aplurality of third regions, each of the plurality of third regions beingdisposed within one of the plurality of second regions or between anadjacent pair of second and having a minimum dimension between 10micrometers and 500 micrometers and threading dislocations with aconcentration between 10³ cm⁻² and 10⁸ cm⁻². The free-standing group IIImetal nitride crystal has a crystallographic miscut that varies by 0.5degrees or less in two orthogonal directions over a central 80% of thecrystal along the first direction and by 0.5 degree or less in twoorthogonal directions over the central 80% of the crystal along a seconddirection orthogonal to the first direction. The at least two domainsare separated by a line of dislocations with a linear density betweenabout 50 cm⁻¹ and about 5×10⁵ cm⁻¹, and a polar misorientation angle γbetween a first domain and a second domain is greater than about 0.005degrees and less than about 0.3 degrees and misorientation angles α andpare greater than about 0.01 degrees and less than about 1 degree.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, may admit to other equally effective embodiments.

FIGS. 1A, 1B, and 1C are simplified diagrams illustrating differentstages of a method of forming a patterned photoresist layer on a seedcrystal or a substrate, according to an embodiment of the presentdisclosure.

FIGS. 1D and 1E are simplified diagrams illustrating a method of forminga patterned mask layer on a seed crystal or a substrate, according to anembodiment of the present disclosure.

FIGS. 1F, 1G, 1H, 1I, and 1J are top views of arrangements of openingsin a patterned mask layer on a seed crystal or a substrate, according toan embodiment of the present disclosure.

FIGS. 1K and 1L are top views of arrangements of openings in a patternedmask layer on a seed crystal or a substrate, according to an embodimentof the present disclosure.

FIGS. 1M and 1N are simplified diagrams illustrating different stages ofa method of forming a patterned photoresist layer on a seed crystal or asubstrate, according to an alternate embodiment of the presentdisclosure.

FIGS. 1O and 1P are simplified diagrams illustrating a method of forminga patterned mask layer on a seed crystal or a substrate, according to analternate embodiment of the present disclosure.

FIG. 1Q is a simplified diagram illustrating a method of formingpatterned trenches within a seed crystal or a substrate, according to anembodiment of the present disclosure.

FIGS. 1R, 1S, and 1T are simplified diagrams illustrating an alternativemethod of forming patterned trenches within a seed crystal or asubstrate, according to an embodiment of the present invention.

FIGS. 2A, 2B, and 2C are simplified diagrams illustrating an epitaxiallateral overgrowth process for forming a large area group III metalnitride crystal, according to an embodiment of the present disclosure.

FIGS. 3A, 3B, and 3C are simplified diagrams illustrating an improvedepitaxial lateral overgrowth process for forming a large area group IIImetal nitride crystal, according to an embodiment of the presentdisclosure.

FIGS. 3D and 3E are simplified diagrams illustrating an improvedepitaxial lateral overgrowth process for forming a large area group IIImetal nitride crystal, according to an embodiment of the presentdisclosure.

FIGS. 4A, 4B, and 4C are simplified diagrams illustrating a method offorming a free-standing ammonothermal group III metal nitride boule andfree-standing ammonothermal group III metal nitride wafers.

FIGS. 5A-5E are simplified diagrams illustrating first threadingdislocation patterns and regions on individual grains or domains of afree-standing, merged ammonothermal group III metal nitride boule orwafer, according to an embodiment of the present disclosure.

FIGS. 6A-6F are simplified diagrams illustrating second threadingdislocation patterns and regions of a free-standing, mergedammonothermal group III metal nitride boule or wafer, according to anembodiment of the present disclosure.

FIG. 6G illustrates a free-standing, merged ammonothermal group IIInitride boule or wafer characterized by a square pattern and formed byperforming a crystal growth process on an array of tiled seed crystalsthat are configured as shown in FIG. 1G, according to an embodiment ofthe present disclosure.

FIGS. 7A-7D are cross-sectional diagrams illustrating methods andresulting optical and electronic devices, according to embodiments ofthe present disclosure.

FIG. 8 is a top view (plan view) of a free-standing laterally-grown GaNboule or wafer formed by ammonothermal lateral epitaxial growth using amask layer having openings arranged in a two-dimensional square array.

FIGS. 9A, 9B, and 9C are top views of a device structure, for example,of LEDs, according to embodiments of the present disclosure.

FIG. 10 is an optical micrograph of a polished cross section of a trenchin a c-plane GaN substrate that has been prepared, according to anembodiment of the present disclosure.

FIGS. 11A and 11B are optical micrographs of a cross section of ac-plane ammonothermal GaN layer that has formed according to anembodiment of the present disclosure, together with a close-up imagefrom the same cross section.

FIGS. 12A and 12B are plan-view optical micrographs of c-planeammonothermal GaN layers that have been subjected to defect-selectiveetching, showing a low concentration of etch pits in the window regionabove slit-shaped mask openings oriented along a <10-10> direction and alinear array of etch pits (threading dislocations) at coalescence frontsformed approximately midway between two window regions, according to twoembodiments of the present disclosure.

FIG. 13 is a summary of x-ray diffraction measurements comparing themiscut variation across a 50 mm wafer fabricated according to oneembodiment of the present disclosure with that of acommercially-available 50 mm wafer.

FIG. 14 is a summary of x-ray rocking-curve measurements comparing thefull-width-at-half-maximum values of two reflections from a 50 mm waferfabricated according to one embodiment of the present disclosure withthat of a commercially-available 50 mm wafer.

FIG. 15 is an optical micrograph of a laser-cut cross section of atrench in a c-plane GaN substrate that has been prepared, according toan embodiment of the present disclosure.

FIG. 16 is a plan-view optical micrograph of a c-plane ammonothermal GaNlayer that has been subjected to defect-selective etching, showing a lowconcentration of etch pits in the window region above slit-shaped maskopenings oriented along a <10-10> direction and a linear array of etchpits (threading dislocations) at coalescence fronts formed approximatelymidway between two window regions, according to an embodiment of thepresent disclosure.

FIGS. 17A-17F are plan views of arrays of seed crystals, according to anembodiment of the current invention.

FIGS. 18A-18D are schematic diagrams of a fixture for holding an arrayof seed crystals during a substrate bulk crystal growth process,according to an embodiment of the current invention.

FIGS. 19A-19D are schematic diagrams of an array of seed crystals atvarious states within a process used to form a tiled compositesubstrate, according to an embodiment of the current invention.

FIG. 19E is a close-up view of a portion of seed crystal within thearray of seed crystals illustrated in FIG. 19B, according to anembodiment of the current invention.

FIG. 19F is a top section-view of a portion of a structure that includesa porous member and polycrystalline GaN layer, as illustrated in FIG.19B, according to an embodiment of the current invention.

FIG. 19G is a top view of a tiled composite substrate, according to anembodiment of the current invention.

FIG. 20A is a schematic diagram of a seed crystal that is adapted foruse in an array of seed crystals, according to an embodiment of thecurrent invention.

FIG. 20B is a top view of a one-dimensional array of seed crystals thatinclude the seed crystal illustrated in FIG. 20A, according to anembodiment of the current invention.

FIG. 20C is an end view of the one-dimensional array of seed crystalsillustrated in FIG. 20B, according to an embodiment of the currentinvention.

FIG. 20D is a top view of the one-dimensional array of seed crystalsillustrated in FIG. 20B after a crystal layer has been grown thereon,according to an embodiment of the current invention.

FIG. 20E is an end view of the one-dimensional array of seed crystalsillustrated in FIG. 20D, according to an embodiment of the currentinvention.

FIG. 21A illustrates lateral sections formed in the one-dimensionalarray of seed crystals illustrated in FIG. 20E by a desirablemanufacturing process, according to an embodiment of the currentinvention.

FIG. 21B is a top view of a one-dimensional array of seed crystals thatis formed using the lateral sections illustrated in FIG. 21A, accordingto an embodiment of the current invention.

FIG. 21C is an end view of the lateral sections of seed crystalsillustrated in FIG. 21B, according to an embodiment of the currentinvention.

FIG. 21D is a top view of the one-dimensional array of seed crystalsillustrated in FIG. 21B after a crystal layer has been grown thereon,according to an embodiment of the current invention.

FIG. 21E is a side view of the one-dimensional array of seed crystalsillustrated in FIG. 21D, according to an embodiment of the currentinvention.

FIG. 22A illustrates lateral sections formed in the one-dimensionalarray of seed crystals illustrated in FIG. 21E by a desirablemanufacturing process, according to an embodiment of the currentinvention.

FIG. 22B is a top view of the one-dimensional array of seed crystalsillustrated in FIG. 22A showing slices performed along coalescencefronts, according to an embodiment of the current invention.

FIG. 22C is a top view of a one-dimensional array of seed crystals thatis formed using a portion of the lateral sections formed by one or moremanufacturing processes described in relation to FIGS. 22A and 22B,according to an embodiment of the current invention.

FIG. 22D is an end view of the one-dimensional array of the seedcrystals illustrated in FIG. 22C, according to an embodiment of thecurrent invention.

FIG. 22E is a top view of the one-dimensional array of seed crystalsillustrated in FIG. 22C after a crystal layer has been grown thereon,according to an embodiment of the current invention.

FIG. 22F is an end view of the one-dimensional array of seed crystalsillustrated in FIG. 22E, according to an embodiment of the currentinvention.

FIGS. 23A-23C are schematic diagrams of a composite substrate at variousstates within a process used to form an electronic device and recoverthe composite substrate, according to an embodiment of the currentinvention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

According to the present disclosure, techniques related to techniquesfor processing materials for manufacture of group-III metal nitride andgallium based substrates are provided. More specifically, embodiments ofthe disclosure include techniques for growing large area substratesusing a combination of processing techniques. In some embodiments of thedisclosure, the large area substrates are referred to herein asfree-standing group III metal nitride wafers. Additionally, in someembodiments, a formed or grown component that is configured to befurther processed to form one or more free-standing group III metalnitride wafers is referred to herein as a free-standing group III metalnitride boule. Merely by way of example, the disclosure can be appliedto growing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, andothers for manufacture of bulk or patterned substrates. Such bulk orpatterned substrates can be used for a variety of applications includingoptoelectronic devices, laser diodes, light emitting diodes,photodiodes, solar cells, photo-electrochemical water splitting andhydrogen generation, photodetectors, integrated circuits, andtransistors, and others.

Threading dislocations in GaN are known to act as strong non-radiativerecombination centers which can severely limit the efficiency ofGaN-based LEDs and laser diodes. Non-radiative recombination generateslocal heating which may lead to faster device degradation (Cao et al.,Microelectronics Reliability, 2003, 43(12), 1987-1991). In high-powerapplications, GaN-based devices suffer from decreased efficiency withincreasing current density, known as droop. There is evidence suggestinga correlation between dislocation density and the magnitude of droop inLEDs (Schubert et al., Applied Physics Letters, 2007, 91(23), 231114).For GaN-based laser diodes there is a well-documented negativecorrelation between dislocation density and mean time to failure (MTTF)(Tomiya et al., IEEE Journal of Selected Topics in Quantum Electronics,2004, 10(6), 1277-1286), which appears to be due to impurity diffusionalong the dislocations (Orita et al., IEEE International ReliabilityPhysics Symposium Proceedings, 2009, 736-740). For electronic devices,dislocations have been shown to markedly increase the leakage current(Kaun et al., Applied Physics Express, 2011, 4(2), 024101) and reducethe device lifetime (Tapajna et al., Applied Physics Letters, 2011,99(22), 223501-223503) in HEMT structures. One of the primary advantagesof using bulk GaN as a substrate material for epitaxial thin film growthis a large reduction in the concentration of threading dislocations inthe film. Therefore, the dislocation density in the bulk GaN substratewill have a significant impact on the device efficiency and thereliability.

Lateral epitaxial overgrowth (LEO) is a method that has been widelyapplied to improvement in the crystallographic quality of films grown byvapor-phase methods. For example, methods whereby GaN layers werenucleated on a sapphire substrate, a SiO₂ mask with a periodic array ofopenings was deposited on the GaN layer, and then GaN was grown bymetalorganic chemical vapor deposition (MOCVD) through the openings inthe SiO₂ mask layer, grew laterally over the mask, and coalesced. Thedislocation density in the areas above the openings in the mask werevery high, similar to the layer below the mask, but the dislocationdensity in the laterally-overgrown regions was orders of magnitude less.This method is attractive because it can be applied to large areasubstrates, significantly reducing their dislocation density. Similarmethods, with variations, have been applied by a number of groups tovapor-phase growth of GaN layers. These methods are variously referredto as LEO, epitaxial lateral overgrowth (ELO or ELOG), selective areagrowth (SAG), and dislocation elimination by epitaxial growth withinverse pyramidal pits (DEEP), or the like. In the case of essentiallyall variations of this method, it is believed that a thinheteroepitaxial GaN layer is grown on a non-GaN substrate, a patternedmask is deposited on the GaN layer, and growth is re-initiated in aone-dimensional or two-dimensional array of openings in the mask. Theperiod or pitch of the growth locations defined by the openings in themask is typically between 2 and 100 micrometers, typically between about5 and 20 micrometers. The individual GaN crystallites or regions growand then coalesce. Epitaxial growth may then be continued on top of thecoalesced GaN material to produce a thick film or “ingot.” A relativelythick GaN layer may be deposited on the coalesced GaN material by HVPE.The LEO process is capable of large reductions in the concentration ofdislocations, particularly in the regions above the mask, typically tolevels of about 10⁵-10⁷ cm⁻². However, very often the laterally-grownwings of the formed LEO layer are crystallographically tilted from theunderlying substrate (“wing tilt”), by as much as several degrees, whichmay be acceptable for a thin-film process but may not be acceptable fora bulk crystal growth process, as it may give rise to stresses andcracking as well as unacceptable variation in surface crystallographicorientation.

Several factors limit the capability of the LEO method, asconventionally applied, to reduce the average dislocation density belowabout 10⁵ to 10⁷ cm⁻², or to reduce the miscut variation across a 50 or100 mm wafer to below about 0.1 degree. First, the pitch of the patternof openings formed in the mask layer tends to be modest, but largerpitches may be desirable for certain applications. Second, c-plane LEOgrowth is generally performed in the (0001), or Ga-face direction, whichcreates at least two limitations. One limitation is that M-directiongrowth rates tend to be lower than those of (0001)-direction growthrates and semipolar (10-11) facets often form, with the consequence thatthe overall crystal diameter decreases with increasing thickness andmaking coalescence of large-pitch patterns difficult. In addition,another limitation is that growth in the (0001) direction tends toexclude oxygen, in contrast to growth in other crystallographicdirections. As a consequence, there may be a significant latticemismatch between a (0001)-grown HVPE crystal used as a seed and thecrystal grown upon it by another technique. In addition, if semipolarfacets form during the LEO process there may be a significant variationin oxygen (or other dopant) level, giving rise to lateral variations inthe lattice constant and stresses that can cause cracking in the LEOcrystal itself or in a crystal grown on the latter, used as a seed.

Variations of the LEO method have been disclosed for other group IIImetal nitride growth techniques besides HVPE. In a first example, Jiang,et al. (U.S. No. 2014/0147650, now U.S. Pat. No. 9,589,792) disclosed aprocess for ammonothermal LEO growth of group-III metal nitrides,replacing the mask layer in typical vapor-phase LEO-type processes (SiO₂or SiN_(x)) by a combination of an adhesion layer, a diffusion-barrierlayer, and an inert layer. In a second example, Mori, et al. (U.S. No.2014/0328742, now U.S. Pat. No. 9,834,859) disclosed a process for LEOgrowth of group-III metal nitrides in a sodium-gallium flux. However, inthis method the coalescing crystallites typically have prominentsemipolar facets, leading to significant lateral variation in theimpurity content of coalesced crystals, and the thermal expansionmismatch between the coalesced nitride layer and a hetero-substrate,which includes a different material than the coalesced nitride layer,may cause uncontrolled cracking.

Several authors, for example, Linthicum et al. (Applied Physics Letters,75, 196, (1999)), Chen et al. (Applied Physics Letters 75, 2062 (1999)),and Wang, et al. (U.S. Pat. No. 6,500,257) have noted that threadingdislocations in growing GaN normally propagate predominantly in thegrowth direction and showed that the dislocation density can be reducedeven more than in the conventional LEO method by growing from thesidewalls of trenches in thin, highly-defective c-plane GaN layersrather than vertically through windows in a patterned mask. Thesemethods have been extended to nonpolar- and semipolar-oriented thin GaNfilms by other authors, for example, Chen et al. (Japanese Journal ofApplied Physics 42, L818 (2003)) and Imer et al. (U.S. Pat. No.7,361,576). However, it is believed that sidewall LEO methods have notyet been extended to growth of bulk GaN, nor to the growth of N-sectorGaN. In particular, we have found that different methods that those usedin the thin film studies work best to form trenches several hundredmicrons deep with pitches on the millimeter scale and produce someunexpected benefits.

FIGS. 1A-1T are schematic cross-sectional views of a seed crystal or asubstrate during various stages of a method for forming a patterned maskseed layer for ammonothermal sidewall lateral epitaxial overgrowth.Referring to FIG. 1A, a substrate 101 is provided with a photoresistlayer 103 disposed thereon. Substrate 101 and the subsequently formedlayers described in relation to FIGS. 1A-1T can be used in a subsequenttiling operation, as discussed further in relation to FIGS. 2A-2C,3A-3E, and 17A-22F. In certain embodiments, some of the layer formingprocess steps described in relation to FIGS. 1A-1T are performedsubsequently to some of the process steps in a tiling operation, asdiscussed further in relation to FIGS. 17A-F, for example. In certainembodiments, substrate 101 consists of or includes a substrate materialthat is a single-crystalline group-III metal nitride, gallium-containingnitride, or gallium nitride. The substrate 101 may be grown by HVPE,ammonothermally, or by a flux method. One or both large area surfaces ofsubstrate 101 may be polished and/or chemical-mechanically polished. Alarge-area surface 102 of substrate 101 may have a crystallographicorientation within 5 degrees, within 2 degrees, within 1 degree, orwithin 0.5 degree of (0001) +c-plane, (000-1) −c-plane, {10-10} m-plane,{11-2±2}, {60-6±1}, {50-5±1}, {40-4±1}, {30-3±1}, {50-5±2}, {70-7±3},{20-2±1}, {30-3±2}, {40-4±3}, {50-5±4}, {10-1±1}, {1 0 −1 ±2}, {1 0 −1±3}, {2 1 −3 ±1}, or {3 0 −3 ±4}. It will be understood that plane {3 0−3 ±4} means the {3 0 −3 4} plane and the {3 0 −3 −4} plane. Large-areasurface 102 may have an (h k i l) semipolar orientation, where i=−(h+k)and l and at least one of h and k are nonzero. Large-area surface 102may have a maximum lateral dimension between about 5 millimeters andabout 600 millimeters and a minimum lateral dimension between about 1millimeter and about 600 millimeters and substrate 101 may have athickness between about 10 micrometers and about 10 millimeters, orbetween about 100 micrometers and about 2 millimeters.

Substrate 101 may have a surface threading dislocation density less thanabout 10⁷ cm⁻², less than about 10⁶ cm⁻², less than about 10⁵ cm⁻², lessthan about 10⁴ cm⁻², less than about 10³ cm⁻², or less than about 10²cm⁻². Substrate 101 may have a stacking-fault concentration below about10⁴ cm⁻¹, below about 10³ cm⁻¹, below about 10² cm⁻¹, below about 10cm⁻¹ or below about 1 cm⁻¹. Substrate 101 may have a symmetric x-rayrocking curve, for example, (002) in the case of c-plane, full width athalf maximum (FWHM) less than about 500 arcsec, less than about 300arcsec, less than about 200 arcsec, less than about 100 arcsec, lessthan about 50 arcsec, less than about 35 arcsec, less than about 25arcsec, or less than about 15 arcsec. Substrate 101 may have anon-symmetric x-ray rocking curve, for example, (201) in the case ofc-plane, full width at half maximum (FWHM) less than about 500 arcsec,less than about 300 arcsec, less than about 200 arcsec, less than about100 arcsec, less than about 50 arcsec, less than about 35 arcsec, lessthan about 25 arcsec, or less than about 15 arcsec. Substrate 101 mayhave a crystallographic radius of curvature greater than 0.1 meter,greater than 1 meter, greater than 10 meters, greater than 100 meters,or greater than 1000 meters, in at least one, at least two, or in threeindependent or orthogonal directions.

Substrate 101 may comprise regions having a relatively highconcentration of threading dislocations separated by regions having arelatively low concentration of threading dislocations. Theconcentration of threading dislocations in the relatively highconcentration regions may be greater than about 10⁵ cm⁻², greater thanabout 10⁶ cm⁻², greater than about 10⁷ cm⁻², or greater than about 10⁸cm⁻². The concentration of threading dislocations in the relatively lowconcentration regions may be less than about 10⁶ cm⁻², less than about10⁵ cm⁻², or less than about 10⁴ cm⁻². Substrate 101 may compriseregions having a relatively high electrical conductivity separated byregions having a relatively low electrical conductivity. Substrate 101may have a thickness between about 10 microns and about 100 millimeters,or between about 0.1 millimeter and about 10 millimeters. Substrate 101may have a maximum dimension, including a diameter, of at least about 5millimeters, at least about 10 millimeters, at least about 25millimeters, at least about 50 millimeters, at least about 75millimeters, at least about 100 millimeters, at least about 150millimeters, at least about 200 millimeters, at least about 300millimeters, at least about 400 millimeters, or at least about 600millimeters.

Large-area surface 102 (FIG. 1A) may have a crystallographic orientationwithin about 5 degrees of the (000-1) N-face, c-plane orientation, mayhave an x-ray diffraction w-scan rocking curvefull-width-at-half-maximum (FWHM) less than about 200 arcsec less thanabout 100 arcsec, less than about 50 arcsec, or less than about 30arcsec for the (002) and/or the (102) and/or the (201) reflections andmay have an average dislocation density less than about 10⁷ cm⁻², lessthan about 10⁶ cm⁻², less than about 10⁵ cm⁻², or less that about 10⁴cm⁻². In some embodiments, the threading dislocations in large-areasurface 102 are approximately uniformly distributed. In otherembodiments, the threading dislocations in large-area surface 102 arearranged inhomogenously as a one-dimensional array of rows of relativelyhigh- and relatively low-concentration regions or as a two-dimensionalarray of high-dislocation-density regions within a matrix oflow-dislocation-density regions. The crystallographic orientation oflarge-area surface 102 may be constant to less than about 1 degree, lessthan about 0.5 degrees, less than about 0.2 degrees, less than about 0.1degrees, or less than about 0.05 degrees, less than about 0.02 degrees,or less than about 0.01 degrees. In certain embodiments, large-areasurface 102 is roughened to enhance adhesion of a mask layer, forexample, by wet-etching, to form a frosted morphology.

Referring again to FIG. 1A, a photoresist layer 103 may be deposited onthe large-area surface 102 by methods that are known in the art. Forexample, in a certain embodiment of a lift-off process, a liquidsolution of a negative photoresist is first applied to large-areasurface 102. Substrate 101 is then spun at a high speed (for example,between 1000 to 6000 revolutions per minute for 30 to 60 seconds),resulting in a uniform photoresist layer 103 on large-area surface 102.Photoresist layer 103 may then be baked (for example, between about 90and about 120 degrees Celsius) to remove excess photoresist solvent.After baking, the photoresist layer 103 may then be exposed to UV lightthrough a photomask (not shown) to form a patterned photoresist layer104 (FIG. 1B) having a pre-determined pattern of cross-linkedphotoresist, such as regions 104A, formed within the unexposed regions104B. The regions 104B of the patterned photoresist may form stripes ordots having characteristic width or diameter W and pitch L. Thepatterned photoresist layer 104 may then be developed to removenon-cross linked material found in regions 104B and leave regions 104A,such as illustrated in FIG. 1C.

Referring to FIG. 1D, one or more patterned mask layers 111 may bedeposited on large-area surface 102 and regions 104A of the patternedphotoresist layer 104. The one or more patterned mask layers 111 maycomprise an adhesion layer 105 that is deposited on the large-areasurface 102, a diffusion-barrier layer 107 deposited over the adhesionlayer 105, and an inert layer 109 deposited over the diffusion-barrierlayer 107. The adhesion layer 105 may comprise one or more of Ti, TiN,TiN_(y), TiSi₂, Ta, TaN_(y), Al, Ge, Al_(x)Ge_(y), Cu, Si, Cr, V, Ni, W,TiW_(x), TiW_(x)N_(y), or the like and may have a thickness betweenabout 1 nanometer and about 1 micrometer. The diffusion-barrier layer107 may comprise one or more of TiN, TiN_(y), TiSi₂, W, TiW_(x),TiN_(y), WN_(y), TaN_(y), TiW_(x)N_(y), TiW_(x)Si_(z)N_(y), TiC, TiCN,Pd, Rh, Cr, or the like, and have a thickness between about 1 nanometerand about 10 micrometers. The inert layer 109 may comprise one or moreof Au, Ag, Pt, Pd, Rh, Ru, Ir, Ni, Cr, V, Ti, or Ta and may have athickness between about 10 nanometers and about 100 micrometers. The oneor more patterned mask layers 111 may be deposited by sputterdeposition, thermal evaporation, electron-beam evaporation, or the like.After deposition of the patterned mask layer(s) 111, the portions of thepatterned mask layer(s) 111 residing above the regions 104A of thepatterned photoresist layer 104 are not in direct contact with thesubstrate 101, as shown in FIG. 1D. The regions 104A and portions of thepatterned mask layer(s) 111 disposed thereon are then lifted off bymethods that are known in the art to form the openings 112 in thepatterned mask layer(s) 111, as shown in FIG. 1E. In certainembodiments, a relatively thin inert layer, for example, 10 to 500nanometers thick, is deposited prior to the lift-off process. Afterperforming the lift-off process, an additional, thicker inert layer, forexample, 5 to 100 micrometers thick, may be deposited over thealready-patterned inert layer by electroplating, electroless deposition,or the like.

Other methods besides the lift-off procedure described above may be usedto form the patterned mask layer 111, including shadow masking, positiveresist reactive ion etching, wet chemical etching, ion milling, andnanoimprint lithography, plus variations of the negative resist lift-offprocedure described above.

In certain embodiments, patterned mask layer(s) 111 are deposited onboth the front and back surfaces of substrate 101.

FIGS. 1F-1L are top views of arrangements of exposed regions 120 on thesubstrate 101 formed by one or more of the processes described above.The exposed regions 120 (or also referred to herein as growth centers),which are illustrated, for example, in FIGS. 1F-1L, may be defined bythe openings 112 formed in patterned mask layer(s) 111 shown in FIG. 1E.In certain embodiments, the exposed regions 120 are arranged in aone-dimensional (1D) array in the y-direction, such as a single columnof exposed regions 120 as shown in FIG. 11 . In certain embodiments, theexposed regions 120 are arranged in a two-dimensional (2D) array in x-and y-directions, such as illustrated in FIGS. 1F-1H and 1J-1L. Theopenings 112, and thus exposed regions 120, may be round, square,rectangular, triangular, hexagonal, or the like, and may have an openingdimension or diameter W between about 1 micrometer and about 5millimeters, or between about 10 micrometers and about 500 micrometerssuch as illustrated in FIGS. 1F-1I. The exposed regions 120 may bearranged in a 2D hexagonal or square array with a pitch dimension Lbetween about 5 micrometers and about 20 millimeters, between about 200micrometers and about 15 millimeters, or between about 500 micrometersand about 10 millimeters, or between about 0.8 millimeter and about 5millimeters, such as illustrated in FIGS. 1F and 1G. The exposed regions120 may be arranged in a 2D array, in which the pitch dimension L₁ inthe y-direction and pitch dimension L₂ in the x-direction may bedifferent from one another, as illustrated in FIGS. 1H and 1J-1L. Theexposed regions 120 may be arranged in a rectangular, parallelogram,hexagonal, or trapezoidal array (not shown), in which the pitchdimensions L₁ in the y-direction and L₂ in the x-direction may bedifferent from one another, as illustrated in FIGS. 1H and 1J-1L). Thearray of exposed regions 120 may also be linear or irregular shaped. Theexposed regions 120 in patterned mask layer(s) 111 may be placed inregistry with the structure of substrate 101. For example, in certainembodiments, large-area surface 102 is hexagonal, e.g., a (0001) or(000-1) crystallographic orientation, and the openings in patterned masklayer(s) 111 comprise a 2D hexagonal array such that the separationsbetween nearest-neighbor openings are parallel to <11-20> or <10-10>directions in large-area surface 102. In certain embodiments, large-areasurface 102 of the substrate is nonpolar or semipolar and the exposedregions 120 comprise a 2D square or rectangular array such that theseparations between nearest-neighbor openings are parallel to theprojections of two of the c-axis, an m-axis, and an a-axis on large-areasurface 102 of substrate 101. In certain embodiments, the pattern ofexposed regions 120 is obliquely oriented with respect to the structureof substrate 101, for example, wherein the exposed regions 120 arerotated by between about 1 degree and about 44 degrees with respect to ahigh-symmetry axis of the substrate, such as a projection of the c-axis,an m-axis, or an a-axis on large-area surface 102 of substrate 101 thathas a hexagonal crystal structure, such as a Wurtzite crystal structure.In certain embodiments, the exposed regions 120 are substantially linearrather than substantially round. In certain embodiments, the exposedregions 120 are slits having a width W and period L that run across theentire length of substrate 101, as illustrated in FIG. 1I. In certainembodiments, the exposed regions 120 are slits that have a width W₁ inthe y-direction and a predetermined length W₂ in the x-direction that isless than the length of substrate 101 and may be arranged in a 2D lineararray with period L₁ in the y-direction and period L₂ in thex-direction, as illustrated in FIGS. 1J-1L. In some embodiments,adjacent rows of exposed regions 120 (e.g., slits) may be offset in thex-direction from one another rather than arranged directly adjacent, asshown in FIG. 1K. In certain embodiments, the adjacent rows of exposedregions 120 (e.g., slits) may be offset in the longitudinal y-directionfrom one another. In certain embodiments, the exposed regions 120include slits that extend in two or more different directions, forexample, the x-direction and the y-direction, as shown in FIG. 1L. Incertain embodiments, the exposed regions 120 (e.g., slits) may bearranged in a way that reflects the hexagonal symmetry of the substrate.In certain embodiments, the exposed regions 120 (e.g., slits) may extendto the edge of the substrate 101.

In certain embodiments, the pattern of openings is terminated by apredetermined distance from the edge of the substrate, for example, by adistance between 10 micrometers and 5 millimeters, between 20micrometers and 2 millimeters, between 50 micrometers and 1 millimeter,or between 100 micrometers and 500 micrometers. The termination of thepattern(s) form a rim that surrounds the edge of the substrate. The rimcan have a width equal to the predetermined distance, which can be usedto improve the integrity and robustness of the edges of the patternedmask layers, for example. The rim, as well as the edges of thesubstrate, may be covered by patterned mask layers 111.

In an alternative embodiment, as shown in FIG. 1M, large-area surface102 of substrate 101 is covered with a blanket mask 116, comprising one,two, or more of adhesion layer 105, diffusion-barrier layer 107, andinert layer 109, followed by a positive photoresist layer 113. Thephotoresist layer is exposed to UV light through a photomask (notshown), forming solubilizable, exposed regions 106B and unexposedregions 106A, as shown in FIG. 1N (essentially the negative of thepattern shown in FIG. 1B). Exposed regions 106B are then removed bydeveloping. As shown in FIG. 1O, openings 112 in the blanket mask 116(comprising adhesion layer 105, diffusion-barrier layer 107, and inertlayer 109) may then be formed by wet or dry etching through the openingsin patterned photoresist layer 113A, to form the patterned mask layer111. After forming the openings 112 the photoresist layer 113 isremoved, as shown in FIG. 1P, producing a structure that is similar oridentical to that shown in FIG. 1E.

Trenches 115 are then formed in exposed regions 120 of the substrate 101through the openings 112 (or “windows”) formed in patterned mask layer111, as shown in FIG. 1Q. In certain embodiments, the depth of thetrenches 115 is between 50 micrometers and about 1 millimeter or betweenabout 100 micrometers and about 300 micrometers. In certain embodimentsthe trenches 115 penetrate the entire thickness of substrate 101,forming patterned holes or slits that extend from the rear side 118 ofthe substrate 101 and through the openings 112 of the patterned masklayer 111. The width of an individual trench may be between about 10micrometers and about 500 micrometers, or between about 20 micrometersand about 200 micrometers. Individual trenches 115 may be linear orcurved and may have a length in the X-direction and/or Y-directionbetween about 100 micrometers and about 50 millimeters, or between about200 micrometers and about 10 millimeters, or between about 500micrometers and about 5 millimeters. In a specific embodiment,large-area surface 102 of substrate 101 has a (000-1), N-faceorientation and trench 115 is formed by wet etching. In a specificembodiment, an etchant composition or solution comprises a solution of85% phosphoric acid (H₃PO₄) and sulfuric (H₂SO₄) acids with aH₂SO₄/H₃PO₄ ratio between 0 and about 1:1. In certain embodiments, aphosphoric acid solution is conditioned to form polyphosphoric acid,increasing its boiling point. For example, reagent-grade (85%) H₃PO₄ maybe conditioned by stirring and heating in a beaker at a temperaturebetween about 200 degrees Celsius and about 450 degrees Celsius forbetween about 5 minutes and about five hours. In a specific embodiment,trench 115 is formed by heating masked substrate 101 in one of theaforementioned etch solutions at a temperature between about 200 degreesCelsius and about 350 degrees Celsius for a time between about 15minutes and about 6 hours. In another embodiment, trench 115 is formedby electrochemical wet etching.

FIGS. 1R-1T show an alternative approach to forming an array ofpatterned, masked trenches in substrate 101. A blanket mask 116(comprising adhesion layer 105, diffusion-barrier layer 107, and inertlayer 109) may be deposited on large-area surface 102 of substrate 101as shown in FIG. 1R. Nascent trenches 114 may be formed by laserablation, as shown in FIG. 1S, to form a patterned mask layer 111. Thelaser ablation process is also known as or referred to as lasermachining or laser beam machining processes. Laser ablation may beperformed by a watt-level laser, such as a neodymium-dopedyttrium-aluminum-garnet (Nd:YAG) laser, a CO₂ laser, an excimer laser, aTi:sapphire laser, or the like. The laser may emit pulses with a pulselength in the nanosecond, picosecond, or femtosecond range. In certainembodiments the frequency of the output light of the laser may bedoubled, tripled, or quadrupled using an appropriate nonlinear optic.The beam width, power, and scan rate of the laser over the surface ofsubstrate 101 with patterned mask layer 111 may be varied to adjust thewidth, depth, and aspect ratio of nascent trenches 114. The laser may bescanned repetitively over a single trench or repetitively over the wholearray of trenches.

The surfaces and sidewalls of the nascent trenches 114 may containdamage left over from the laser ablation process. In certainembodiments, substrate 101, containing nascent trenches 114, is furtherprocessed by wet etching, dry etching, or photoelectrochemical etchingin order to remove residual damage in nascent trenches 114. In aspecific embodiment, large-area surface 102 of substrate 101 has a(000-1), N-face orientation and a trench 115 is formed from nascenttrench 114 by wet etching as shown in FIG. 1T. In a specific embodiment,an etchant composition or solution comprises a solution of 85%phosphoric acid (H₃PO₄) and sulfuric (H₂SO₄) acids with a H₂SO₄/H₃PO₄ratio between 0 and about 1:1. In certain embodiments, a phosphoric acidsolution is conditioned to form polyphosphoric acid, increasing itsboiling point. For example, reagent-grade (85%) H₃PO₄ may be conditionedby stirring and heating in a beaker at a temperature between about 200degrees Celsius and about 450 degrees Celsius for between about 5minutes and about five hours. In a specific embodiment, trench 115 isformed by heating substrate 101 in one of the aforementioned etchsolutions at a temperature between about 200 degrees Celsius and about350 degrees Celsius for a time between about 15 minutes and about 6hours.

After performing one or more of the processes described above on thesubstrate 101, a crystal growth process can be performed on a singlesubstrate 101 or on an array of substrates 101 at the same time. Thesingle substrate 101 or array of substrates 101 act as a seed crystal orseed crystals, respectively, during the crystal growth process. FIGS.17A-17F illustrate some examples of various arrays of seed crystals 370,such as substrates 101, which can be used during a crystal growthprocess. Referring to FIGS. 17A-17F, at least some of the edges 395 oftwo or more seed crystals 370 are prepared for tessellation to form aone- or two-dimensional array of tile crystals. The seed crystals 370may each be prepared in a square shape (FIG. 17A), a rectangular shape(FIG. 17B), a hexagonal shape (FIG. 17C), a mix of a rhombus and atriangular shape (FIG. 17D), a mix of a hexagonal and a pentagonal shape(FIG. 17E), a mix of a hexagonal and a rhombus shape (FIG. 17F), orother shapes, or combinations thereof. Square or rectangular shapes maybe preferred when surface 102 has a nonpolar or semipolar orientation.Hexagonal, rhombus, triangular, rhombohedral, pentagonal, or trapezoidalshapes may be preferred when surface 102 has a (000±1) c-planeorientation. Triangular, tetragonal, or pentagonal shapes may be usefulfor defining the outer perimeter of the array of seed crystals. Incertain embodiments, some or all of the edges 395 of the seed crystals370 are prepared such that the intersection of the edge with large-areasurface 102 is parallel, to within 0.5 degree, 0.2 degree, 0.1 degree,0.05 degree, 0.02 degree, or 0.01 degree, to a plane chosen from {11-20}a-plane, (000±1) c-plane, {10-10} m-plane, {10-1±1}, or a plane definedby a perpendicular to large-area surface 102 and an axis chosen from thec-axis, an m-axis, or an a-axis. In certain embodiments, the edges 395are prepared with a root-mean-square surface roughness that is less than10 micrometers, less than 5 micrometers, less than 2 micrometers, orless than 1 micrometer. In certain embodiments, the edges 395 areprepared prior to pattern deposition and patterning, as described aboveand in FIGS. 1A-1T, so that patterned mask layer 111 extends fromlarge-area surface 102 over at least a portion of the edges. In certainembodiments, edges 395 are prepared by at least one of a dicing saw, awire saw, and a laser. In certain embodiments, the edges 395 alsoinclude an orientation flat, such as missing corner, or an orientationgroove, so as to simplify tracking of the crystallographic orientationof each seed crystal 370.

In certain embodiments, many, most, or all of the seed crystals 370positioned in an array are prepared such that they have, accurately, thesame size and shape. For example, the X-direction dimensions 380 of eachof the nominally-identical seed crystals 370 in the array may be equalto within 0.5 millimeter, 0.2 millimeter, 0.1 millimeter, 50micrometers, 20 micrometers, 10 micrometers, 5 micrometers, 2micrometers, or 1 micrometer. In certain embodiments, X-directiondimension 380 is between 4 millimeters and 10 millimeters, between 10millimeters and 15 millimeters, between 15 millimeters and 25millimeters, between 25 millimeters and 50 millimeters, between 50millimeters and 100 millimeters, or between 100 millimeters and 150millimeters. Similarly, the Y-direction dimensions 390 of each of thenominally-identical seed crystals in the array may be equal to within0.5 millimeter, 0.2 millimeter, 0.1 millimeter, 50 micrometers, 20micrometers, 10 micrometers, 5 micrometers, 2 micrometers, or 1micrometer. In certain embodiments, Y-direction dimension 390 is between8 millimeters and 10 millimeters, between 10 millimeters and 15millimeters, between 15 millimeters and 25 millimeters, between 25millimeters and 50 millimeters, between 50 millimeters and 100millimeters, or between 100 millimeters and 150 millimeters. In certainembodiments, some of the edges 395, specifically, the outward-facingedges in the array of seed crystals, may be cut to be circular orelliptical sections, rather than straight lines, in order to enable acurved or approximately circular or elliptical perimeter of the array ofseed crystals 370, as illustrated in FIG. 19G. In certain embodiments,the starting point for seed crystals 370 are wafers, with apredominantly round perimeter, and portions of the original edges areretained while other edges are prepared as described above fortessellation.

In certain embodiments, a backside and, optionally, one or more edgesand/or a front side, of one or more seed crystals is coated with amechanically-compliant coating, or interfacial layer 1921 (FIG. 19E),which is configured to accommodate any extrinsic or intrinsic stressformed between the seed crystal 370 and deposited layers or structuresdisposed thereon without either the seed crystal 370 or the depositedlayers or structures undergoing cracking or other failure. Themechanically-compliant coating may include or consist of one or more ofgraphite, pyrolytic graphite, boron nitride, pyrolytic boron nitride,molybdenum disulfide, and tungsten disulfide. In certain embodiments,the mechanically-compliant coating is deposited by at least one ofsputtering, chemical vapor deposition, plasma-enhanced chemical vapordeposition, high density plasma chemical vapor deposition, andelectron-beam evaporation. In certain embodiments, themechanically-compliant coating is not fully dense and is deposited byone or more of spraying particles suspended in a slurry, screen printingof particles suspended in a slurry, painting of particles suspended in aslurry, plasma spraying, or the like. In certain embodiments themechanically-compliant coating is subjected to a heat treatment processto partially or fully sinter particles in the mechanically-compliantcoating.

In some embodiments, the thicknesses of each of seed crystals 370 areequal, to within 50 micrometers, to within 25 micrometers, to within 10micrometers (μm), to within 5 micrometers, to within 2 micrometers, orto within 1 micrometer. In certain embodiments, a uniform seed thicknesswill improve the mechanical integrity of a clamped array of seedcrystals. In certain embodiments, a uniform seed thickness will enhancethe co-planarity of the top surface of the seed crystals. In certainembodiments, a uniform seed thickness may enhance both the mechanicalintegrity and thermal uniformity of the composite structure beingfabricated. The crystallographic miscut of each of the large-areasurfaces 102 of seed crystals 370 has a magnitude and a direction 397.For example, if a particular c-plane seed crystal is miscut by 0.50degrees in the in-direction and by 0.06 degrees in an orthogonala-direction, the magnitude of the miscut is approximately 0.504 degreesand its direction is 6.8 degrees away from a particular in-direction. Insome embodiments, the magnitudes of each of the crystallographic miscutsof seed crystals 370 are equal, within 0.2 degree, within 0.1 degree,within 0.05 degree, within 0.02 degree, or within 0.01 degree. In someembodiments, the directions 397 of the crystallographic miscuts of eachof the seed crystals are aligned to within 10 degrees, within 5 degrees,within 2 degrees, within 1 degree, within 0.5 degree, within 0.2 degree,or within 0.1 degree.

In certain embodiments, an array of seed crystals 370 is placed in amechanical fixture, as shown schematically in FIGS. 18A-18D. Thisembodiment may be suitable when there are small number of seed crystals,or when each seed crystal can be held in place by clamping a portion ofthe periphery of each seed crystal in the array of seed crystals. Forexample, this technique may be used with the seed crystal arrays shownin FIGS. 17E and 17F, but not with the seed crystal arrays shown inFIGS. 17A-D. The seed crystals 370 may be placed on a backing plate 1810(FIG. 18A), a retaining ring 1830 (FIG. 18B) may be placed around theperimeter of the array of seed crystals 370, and a clamp ring 1840 (FIG.18C) may be placed on top of retaining ring 1830. Each of backing plate1810, retaining ring 1830, and clamp ring 1840 may have three or morethrough-holes 1820, 1825 for attachment by a set of fasteners, such asscrews, bolts, or threaded rods. In certain embodiments through-holes1820 are tapped while through-holes 1825 are bored through. In preferredembodiments, each of backing plate 1810, retaining ring 1830, and clampring 1840 are fabricated from a material having a coefficient of thermalexpansion (CTE) that is slightly smaller than that of seed crystals 370,such as molybdenum. In certain embodiments, through-holes 1820 arelocated to the periphery of seed crystals 370. In certain embodiments,at least one seed crystal 370 is penetrated by a through-hole that isaligned with a least one through-hole 1820 or 1825 in backing plate1810. In certain embodiments, one or more of backing plate 1810,retaining ring 1830, and clamp ring 1840 may be coated with a releasecoating to simplify removal of a merged crystal from the fixturecomponents. In certain embodiments, the release coating inhibitsdeposition or adhesion of GaN on the mechanical components. In certainembodiments, the release coating provides mechanical compliance betweenthe seed crystal and the fixture components, accommodating stress due toresidual CTE mismatch without cracking or failure. The release coatingmay include or consist of one or more of graphite, boron nitride,molybdenum disulfide, or tungsten disulfide. In certain embodiments, therelease coating is not fully dense and is deposited by one or more ofspraying particles suspended in a slurry, screen printing of particlessuspended in a slurry, painting of particles suspended in a slurry, orthe like.

In some embodiments, it is desirable to form at least some portion ofthe mechanical fixture out of molybdenum (Mo), since Mo is known to havea CTE of approximately 5.8×10⁻⁶/K, when averaged over the temperaturerange of 20 degrees Celsius and 1000 degrees Celsius. In someembodiments the alloy of Mo is chosen such that its recrystallizationtemperature exceeds the maximum temperature that the mechanical fixturewill reach during the crystal growth process. If the recrystallizationtemperature is exceeded during processing, grain growth can occur in theMo substrate resulting in changes in the stress state of the material,which can lead to embrittlement of the material after it is subsequentlycooled. Doping of Mo with Titanium and Zirconium to produce what iscommercially referred to as titanium-zirconium-molybdenum (TZM) alloy,is known to increase the recrystallization temperature relative to Mo tothe range of 1200 degrees Celsius to 1400 degrees Celsius, which is 200degrees Celsius to 300 degrees Celsius higher than the recrystallizationtemperature of elemental Mo and 100 degrees Celsius to 600 degreesCelsius higher than the epitaxial growth temperature. TZM is a dilutealloy of Mo (greater than 98% and preferably at least 99%), Ti (between0.2% and 1.0%), Zr (between 0% and 0.3%), and C (between 0% and 0.1%).Other alloys are also possible. For example, the CTE of alloys of MoW,averaged over the temperature range of 20-1000 degrees Celsius, can beengineered to fall in the range of 4.9×10⁻⁶/K and 5.8×10⁻⁶/K. The CTE ofthe mechanical fixture component material may be engineered to bebetween 80% and 99%, between 85% and 98%, between 90 and 97%, or between94% and 96% of the CTE of the crystals in the plane of the firstsurface.

The flatness of the mechanical fixture components is such that theamount of warp across their diameter should not exceed 0.1% of theirdiameter, and preferably should not exceed 0.02%. Warp is herein definedas the sum of the maximum positive and maximum negative deviation of thefixture component top surface from an imaginary flat plane, where theimaginary flat plane is selected to be that plane which intersects thefixture component top surface and minimizes the magnitude of the warp.

The clearance between the retaining ring and the array of seed crystals370 may be chosen so that the clearance shrinks to nearly zero at apredetermined temperature used for bulk crystal growth, causing each ofthe seed crystals 370 to be positioned so that there is little to no gapbetween adjacent edges of neighbors, ensuring accurate crystallographicalignment of the seed crystals 370. In one example, the gap 1711 (FIGS.17A-17F) between adjacent edges of the seed crystals 370 is between zeroand 200 micrometers, between 0.1 micrometer and 50 micrometers, orbetween 0.2 micrometer and 50 micrometers. In certain embodiments, eachof backing plate 1810, retaining ring 1830, and clamp ring 1840 isfabricated from molybdenum or a molybdenum alloy, such as MoW or TZM orsilver-clad Mo, W, or Ni. In certain embodiments, the materials used toprepare at least one of backing plate 1810, retaining ring 1830, andclamp ring 1840 are annealed to remove residual stresses beforemachining. In certain embodiments, mesa structures are incorporated intobacking plate 1810 at positions of the intersections of two, three ormore seed crystals. In certain embodiments, the tops of the mesas areground to be accurately flat and co-planar, so as to improve thealignment accuracy or planarity of a surface of the seed crystals 370that is parallel to the flat or co-planar surfaces of the mesas. Incertain embodiments, additional components are incorporated into themechanical fixture, such as spacer pads or springs. The additionalcomponents may be fabricated from materials that are compatible with anammonothermal crystal growth environment, such as at least one ofmolybdenum, tungsten, tantalum, niobium, silver, gold, platinum, oriridium.

After assembling the array of seed crystals in the fixture, the fixturemay be fastened together using at least three screws, bolts, threadedrod and nuts, or similar fasteners 1855 to form tiled array 1860 (FIG.18D).

The mechanical fixture is designed and fabricated in such a way that thecrystallographic orientations between each of the group III nitridecrystals positioned on the fixture, or positioned within the fixture,are substantially identical. Referring again to FIG. 18D, firstcoordinate system 1821 (x₁ y₁ z₁) represents the crystallographicorientation of a first group III nitride crystal 1801, where z₁ is thenegative surface normal of the nominal orientation of the surface 1811of first group III nitride crystal 1801, and x₁ and y₁ are vectors thatare orthogonal to z₁. For example, if surface 1801 has a (0 0 0 1)orientation, then z₁ is a unit vector along [0 0 0 −1], and x₁ and y₁may be chosen to be along [1 0 −1 0] and [1 −2 1 0], respectively. Ifsurface 1811 has a (1 0 −1 0) orientation, then z₁ is a unit vectoralong [−1 0 1 0] and x₁ and y₁ may be chosen to be along [1 −2 1 0] and[0 0 0 1], respectively. Similarly, second coordinate system 1822 (x₂ y₂z₂) represents the crystallographic orientation of the second nitridecrystal 1802, where z₂ is the negative surface normal of the nominalorientation of surface 1812 of second nitride crystal 1802 and x₂ and y₂are vectors that are orthogonal to z₂, where the same convention is usedfor the crystallographic directions corresponding to (x₂ y₂ z₂) as for(x₁ z₁). The crystallographic misorientation between the surface offirst nitride crystal and the surface of second nitride crystal may bespecified by the three angles α, β, and γ, where a is the angle betweenx₁ and x₂, β is the angle between y₁ and y₂, and γ is the angle betweenz₁ and z₂. Because the surface orientations of the first and secondnitride crystals are nearly identical, the polar misorientation angle γis very small, for example, less than 0.5 degree, less than 0.2 degree,less than 0.15 degree, less than 0.1 degree, less than 0.05 degree, lessthan 0.02 degree, or less than 0.01 degree. Because of the precisecontrol in the orientation of the nitride crystals during placement, themisorientation angles α and β are also very small, for example, lessthan 1 degree, less than 0.5 degree, less than 0.2 degree, less than 0.1degree, less than 0.05 degree, less than 0.02 degree, or less than 0.01degree. Typically, γ will be less than or equal to α and β. Thecrystallographic misorientation between additional, adjacent nitridecrystals is similarly very small. However, the crystallographicmisorientation angles α, β, and γ may be detectable by x-raymeasurements and may be greater than about 0.005 degree, greater thanabout 0.01 degree, greater than about 0.02 degree, greater than about0.05 degree, greater than about 0.1 degree, or greater than about 0.2degree.

In the embodiment described above the mechanical fixture supporting thearray of seed crystals may have a CTE that is similar to, but slightlyless than, the CTE of the seed crystals themselves. In anotherembodiment, a polycrystalline group III nitride containing supportingstructure is used in place of the molybdenum material in the mechanicalfixture. The polycrystalline group III nitride may be textured or highlytextured. Since the CTE of GaN differs by approximately 12% between thea and c directions, for example, polycrystalline GaN will not have aprecise CTE match to single-crystal GaN seed crystals. However, themismatch is small and the temperature dependence of the CTE in the a andc directions are similar. In addition, in the limit that thepolycrystalline GaN material is highly textured in the c-direction, itsCTE in the lateral direction will closely approximate the CTE ofsingle-crystal GaN in the a-direction. Exemplary methods for fabricatingtextured, polycrystalline group III metal nitride are described in U.S.Pat. No. 8,039,412 8,461,071, RE47114, 10,094,017, and 10,619,239, eachof which is incorporated by reference in its entirety.

In certain embodiments, used to support an array of seed crystals 370during processing, the array of seed crystals 370 is placed on asupporting surface 1915 of a susceptor 1910, as shown in FIG. 19A. Thisembodiment may be suitable for each of the seed arrays shownschematically in FIGS. 17A-F. In some embodiments, a spacer (not shown)of a desired size is disposed between the adjacent edges of each of theseed crystals 370 so that a defined and regular spacing can bemaintained in at least one direction, such as the X-direction, or eventhe X-direction and the Y-direction. The spacer may include a machinedblock or a wire of a desired diameter. The spacing between adjacentedges of each of the seed crystals 370 may be set such that the spacingis less than 2 millimeters (mm), such as such as between 0.1 micrometer(μm) and 1 millimeters (mm), or between 0.1 micrometer and 200micrometers, between 0.1 micrometer and 50 micrometers, or between 0.2micrometer and 50 micrometers.

Susceptor 1910 may include or consist of one or more of SiO₂, graphite,pyrolytic boron nitride (PBN), SiC-coated graphite, PBN-coated graphite,TaC-coated graphite, molybdenum, or molybdenum alloy. In certainembodiments, a surface 1915 of susceptor 1910 facing one or more seedcrystals may be coated with a release coating 1923, as shownschematically in FIG. 19E. The release coating 1923 may include orconsist of one or more of graphite, boron nitride, molybdenum disulfide,or tungsten disulfide. In certain embodiments, the release coating 1923is not fully dense and is deposited by one or more of spraying particlessuspended in a slurry, screen printing of particles suspended in aslurry, painting of particles suspended in a slurry, or the like. Incertain embodiments the array of seed crystals 370 is surrounded by aretainer ring 1930 that is disposed over the supporting surface 1915. Incertain embodiments, retainer ring 1930 includes or consists of amaterial with a slightly smaller CTE than GaN, for example, molybdenumor a molybdenum alloy. In certain embodiments susceptor 1910 is machinedto have hollow regions or formed depressions in the supporting surface1915 that are formed in the shapes of seed crystals 370 in order tofacilitate accurate alignment of the seed crystals and crystal planesformed therein to one another. In certain embodiments, retainer ring1930 includes or consists of a wire. In certain embodiments, a largearea surface of one or more seed crystals having amechanically-compliant coating (e.g., interfacial layer 1921 in FIG.19E) formed therebetween is placed in contact with the supportingsurface 1915 of the susceptor 1910. In certain embodiments, a large areasurface of one or seed crystals having a mechanically-compliant coating(e.g., interfacial layer 1921) is positioned on a side that is oppositeto the supporting surface 1915 of the susceptor 1910. Themechanically-compliant coating is used to relieve some of the extrinsicand intrinsic stress formed between the seed crystal(s) 370 and thesusceptor 1910 and/or the seed crystal(s) 370 and a porous member 1940and/or polycrystalline GaN layer 1950 disposed on an opposing side,which are discussed below.

In certain embodiments, a porous member 1940 is placed over one or moreof the seed crystals 370, and is configured to minimize the extrinsicstress induced in the seed crystals 370 due to the CTE mismatch createdbetween the seed crystals 370 and the porous member 1940. The porousmember 1940 is also useful to reduce the stress induced in the seedcrystals 370 due to the CTE mismatch created between the seed crystals370 and a subsequently deposited polycrystalline GaN layer 1950 formedthereover. In certain embodiments, porous member 1940 has a honeycombstructure, as illustrated in FIG. 19F. The porous member 1940 mayinclude or consist of one or more of graphite, carbon fiber, silicafiber, aluminosilicate fiber, borosilicate fiber, a silicon carbidecoating, a pyrolytic boron nitride coating, a pyrolytic graphitecoating, or a polymer.

As part of a process used to form a support for the array of seedcrystals 370, the susceptor 1910, with the array of seed crystals 370positioned precisely on it, may be placed into a reactor capable ofpolycrystalline GaN synthesis. The polycrystalline-GaN reactor may thenbe closed, evacuated, and back-filled with nitrogen. The temperature ofthe susceptor 1910 in the reactor may be raised to approximately 900° C.and a bake-out in a mixture of 5% H₂ in N₂ may be performed forapproximately 24 hours to remove oxygen and moisture from the furnace.After the nitrogen bake-out, for example, 1.2 standard liters per minuteof Cl₂ may flowed through a source chamber containing gallium at atemperature of approximately 850 degrees Celsius and the effluent may bemixed with a flow of 15 standard liters per minute of NH₃ in a nitrogencarrier gas. The process may be run for approximately 30 hours, thereactive gases may be stopped, and the reactor may be cooled. Atextured, polycrystalline GaN layer 1950, approximately 1 millimeterthick, may be deposited on the array of seed crystals 370, producing astructure similar to that shown schematically in FIG. 19B. Openings,gaps 1941, or pores within porous member 1940, if present, are partiallyor fully filled with polycrystalline GaN. In certain embodiments, porousmember 1940 becomes completely encased (not shown) withinpolycrystalline GaN. In certain embodiments, one or more components ofporous member 1940, for example, a polymer disposed within the materialused to form the porous member 1940, undergoes partial or completedecomposition during deposition of polycrystalline GaN layer 1950, andthus allows the material within the porous member 1940 to develop one ormore desired mechanical properties.

After forming the polycrystalline GaN layer 1950, the tiled compositestructure 1960, containing seed crystals 370, which are bonded togetherby polycrystalline GaN layer 1950, may then be separated from susceptor1910, as shown schematically in FIG. 19C. As a component of the tiledcomposite structure 1960, which also includes at least the array of seedcrystals 370, the polycrystalline GaN layer 1950 is often referred toherein as a matrix member. While the tiled composite structure 1960 andpolycrystalline GaN layer or matrix member 1950 illustrated in FIGS.19C-19F includes a porous member 1940, this configuration is notintended to limiting as to the scope of the disclosure provided herein.In some embodiments, the matrix member may optionally include the porousmember 1940. In certain embodiments, the susceptor 1910 is separatedfrom tiled composite structure 1960 by use of a mechanical process thatis used to break any bond formed between the susceptor 1910 and thecomponents within the tiled composite structure 1960. In one example, amechanical shear force is applied between the susceptor 1910 and tiledcomposite structure 1960 to causes a portion of a release coating 1923or an interfacial layer 1921, which is disposed therebetween, to crackand fail, and thus allow the susceptor 1910 and tiled compositestructure 1960 to be separated. In other embodiments susceptor 1910 isdissolved, for example, in a mineral acid or base.

In certain embodiments of the tiled composite structure 1960, gaps 1970are formed between adjacent tiled seed crystals 370, as shownschematically in FIG. 19D. The formed gaps 1970 may be helpful duringsubsequent processing steps, such as a merging process, to inhibitgrowth of polycrystalline GaN layer 1950 from interfering with lateralgrowth from seed crystals 370. Gaps 1970 may have a width between about1 micrometer and about 5 millimeters, between about 5 micrometers andabout 1 millimeter, between about 10 micrometer and about 500micrometers, or between about 20 micrometers and about 200 micrometers.Gaps 1970 may have a depth between about 1 micrometer and about 1millimeter, between about 5 micrometers and about 300 micrometers, orbetween about 10 micrometers and about 100 micrometers. Gaps 1970 may beformed by laser machining, for example, a dicing saw, or the like. Incertain embodiments, the gap forming process includes a maskingoperation such that the polycrystalline group III nitride material isprevented from forming between adjacent seed crystals 370 instead of orin addition to etching. In certain embodiments, patterning and etchingof seed crystals 370, as shown schematically in FIGS. 1A-1T, isperformed after formation of tiled composite structure 1960 rather thanbeforehand.

The tile array 1860 and/or tiled composite structure 1960, which includethe array of precisely-oriented seed crystals 370, may then be used as asubstrate for bulk crystal growth, for example, comprising ammonothermalgrowth, HVPE growth, or flux growth. In the discussion below the grownGaN layer will be referred to as an ammonothermal layer, even thoughother bulk growth methods, such as HVPE or flux growth, may be usedinstead. In certain embodiments, comprising ammonothermal bulk growth,one or more tiled arrays 1860 and/or tiled composite structures 1960 maythen be suspended on a seed rack and placed in a sealable container,such as a capsule, an autoclave, or a liner within an autoclave. Incertain embodiments, one or more pairs of tiled arrays are suspendedback to back, with the open and/or patterned large area surfaces facingoutward. A group III metal source, such as polycrystalline group IIImetal nitride, at least one mineralizer composition, and ammonia (orother nitrogen containing solvent) are then added to the sealablecontainer and the sealable container is sealed. The mineralizercomposition may comprise an alkali metal such as Li, Na, K, Rb, or Cs,an alkaline earth metal, such as Mg, Ca, Sr, or Ba, or an alkali oralkaline earth hydride, amide, imide, amido-imide, nitride, or azide.The mineralizer may comprise an ammonium halide, such as NH₄F, NH₄C₁,NH₄Br, or NH₄I, a gallium halide, such as GaF₃, GaCl₃, GaBr₃, GaI₃, orany compound that may be formed by reaction of one or more of F, Cl, Br,I, HF, HCl, HBr, HI, Ga, GaN, and NH₃. The mineralizer may compriseother alkali, alkaline earth, or ammonium salts, other halides, urea,sulfur or a sulfide salt, or phosphorus or a phosphorus-containing salt.The sealable container (e.g., capsule) may then be placed in a highpressure apparatus, such as an internally heated high pressure apparatusor an autoclave, and the high pressure apparatus sealed. The sealablecontainer, containing tiled arrays 1860 and/or tiled compositestructures 1960, is then heated to a temperature above about 400 degreesCelsius and pressurized above about 50 megapascal to performammonothermal crystal growth.

FIGS. 2A-2C illustrate different steps within a bulk crystal growthprocess performed on an array of adjacently-tiled seed crystals, wherethe patterned seed crystals are formed by a LEO process with no trenchesbelow mask openings. During a bulk crystal growth process, group IIImetal nitride layer 213 grows through the openings 112 of patterned masklayer 111, grows outward through the openings, as shown in FIG. 2B,grows laterally over patterned mask layer 111, and coalesces (FIG. 2C),first, between adjacent mask openings and second, between adjacent tileor seed crystals. After coalescence, group III metal nitride layer 213comprises window regions 215, which have grown vertically with respectto the openings in patterned mask layer 111, wing regions 217, whichhave grown laterally over patterned mask layer 111, and firstcoalescence fronts 219, which form at the boundaries between wingsgrowing from adjacent openings in patterned mask layer 111, and secondcoalescence fronts 235, which form at the boundaries between wingsgrowing from adjacent tile or seed crystals. Threading dislocations 214may be present in window regions 215, originating from threadingdislocations that were present at the surface of the substrate 101.

FIGS. 3A-3C illustrate a bulk group III nitride sidewall LEO process.FIGS. 3D-3E illustrate bulk crystal growth on adjacent tiled seedcrystals, where the patterned seed crystals are formed by a sidewall LEOprocess. FIG. 3A illustrates a substrate that includes a patterned,masked trench 115, formed by one of the processes described herein. In asidewall LEO process, a group III metal nitride material 221 grows onthe sides and bottoms of the patterned, masked trenches 115 as shown inFIG. 3B. As group III metal nitride material 221 on the sidewalls oftrenches 115 grow inward, it becomes progressively more difficult forgroup III nitride nutrient material to reach the bottom of the trenches,whether the nutrient material comprises an ammonothermal complex of agroup III metal (in the case of ammonothermal growth), a group III metalhalide (in the case of HVPE), or a group III metal alloy or inorganiccomplex (in the case of flux growth). Eventually group III metal nitridematerial 221 pinches off the lower regions of the trenches, formingvoids 225 as shown in FIG. 3C. It has been found that the concentrationof threading dislocations in group III metal nitride material 221, whichhas grown laterally, is lower than that in substrate 101. Many threadingdislocations 223, originating from substrate 101, terminate on thesurfaces of voids 225. Concomitantly, the group III metal nitride layer213 grows upward through openings 112 (or windows) in patterned masklayer 111. However, since laterally-grown group III metal nitridematerial 221 has a lower concentration of threading dislocations thansubstrate 101 and many dislocations from substrate 101 have terminatedat surfaces of voids 225, the dislocation density in the verticallygrown group III metal nitride layer 213 is considerably reduced,relative to a conventional LEO process, as described above inconjunction with FIG. 2A-2C.

FIGS. 3D-3E illustrate the continuation of the sidewall LEO growthprocess and fusion between adjacent tile or seed crystals. As in theconventional LEO process (FIGS. 2A-2C), group III metal nitride layer213 grows within the openings 112 of patterned mask layer 111, growsoutward through the openings as shown in FIG. 3D, grows laterally overpatterned mask layer 111, and coalesces (FIG. 3E), first, betweenadjacent mask openings and second, between adjacent tile or seedcrystals. After coalescence, group III metal nitride layer 213 compriseswindow regions 215, which have grown vertically with respect to theopenings in patterned mask layer 111, wing regions 217, which have grownlaterally over patterned mask layer 111, and first coalescence fronts219, which form at the boundaries between wings growing from adjacentopenings in patterned mask layer 111, as shown in FIG. 3E, and secondcoalescence fronts 235, which form at the boundaries between wingsgrowing from adjacent tile or seed crystals. Since laterally-grown groupIII metal nitride material 221 has a lower concentration of threadingdislocations than substrate 101 and many threading dislocations fromsubstrate 101 have terminated in voids 225, the concentration ofthreading dislocations in window regions 215 is significantly lower thanin the case of conventional LEO.

Ammonothermal group III metal nitride layer 213 may have a thicknessbetween about 10 micrometers and about 100 millimeters, or between about100 micrometers and about 20 millimeters.

In certain embodiments, ammonothermal group III metal nitride layer 213is subjected to one or more processes, such as at least one of sawing,lapping, grinding, polishing, chemical-mechanical polishing, or etching.

In certain embodiments, the concentration of extended defects, such asthreading dislocations and stacking faults, in the ammonothermal groupIII metal nitride layer 213 may be quantified by defect selectiveetching. Defect-selective etching may be performed, for example, using asolution comprising one or more of H₃PO₄, H₃PO₄ that has beenconditioned by prolonged heat treatment to form polyphosphoric acid, andH₂SO₄, or a molten flux comprising one or more of NaOH and KOH.Defect-selective etching may be performed at a temperature between about100 degrees Celsius and about 500 degrees Celsius for a time betweenabout 5 minutes and about 5 hours, wherein the processing temperatureand time are selected so as to cause formation of etch pits withdiameters between about 1 micrometer and about 25 micrometers, thenremoving the ammonothermal group III metal nitride layer, crystal, orwafer from the etchant solution.

The concentration of threading dislocations in the surface of the windowregions 215 may be less than that in the underlying substrate 101 by afactor between about 10 and about 10⁴. The concentration of threadingdislocations in the surface of the window regions 215 may be less thanabout 10⁸ cm⁻², less than about 10⁷ cm⁻², less than about 10⁶ cm⁻², lessthan about 10⁵ cm⁻², or less than about 10⁴ cm⁻². The concentration ofthreading dislocations in the surface of wing regions 217 may be lower,by about one to about three orders of magnitude, than the concentrationof threading dislocations in the surface of the window regions 215, andmay be below about 10⁵ cm⁻², below about 10⁴ cm⁻², below about 10³ cm⁻²,below about 10² cm⁻², or below about 10 cm⁻². Some stacking faults, forexample, at a concentration between about 1 cm⁻¹ and about 10⁴ cm⁻¹, maybe present at the surface of the window regions 215. The concentrationof stacking faults in the surface of wing regions 217 may be lower, byabout one to about three orders of magnitude, than the concentration ofstacking faults in the surface of the window regions 215, and may bebelow about 10² cm⁻¹, below about 10 cm⁻¹, below about 1 cm⁻¹, or belowabout 0.1 cm⁻¹, or may be undetectable. Threading dislocations, forexample, edge dislocations, may be present at coalescence fronts 219 and235, for example, with a line density that is less than about 1×10⁵cm⁻¹, less than about 3×10⁴ cm⁻¹, less than about 1×10⁴ cm⁻¹, less thanabout 3×10³ cm⁻¹, less than about 1×10³ cm⁻¹, less than about 3×10²cm⁻¹, or less than 1×10² cm⁻¹. The density of dislocations along thecoalescence fronts may be greater than 5 cm⁻¹, greater than 10 cm⁻¹,greater than 20 cm⁻¹, greater than 50 cm⁻¹, greater than 100 cm⁻¹,greater than 200 cm⁻¹, or greater than 500 cm⁻¹.

In certain embodiments, the process of masking and bulk group IIInitride crystal growth is repeated one, two, three, or more times. Insome embodiments, these operations are performed while the first bulkgroup III metal nitride layer remains coupled to substrate 101. In otherembodiments, substrate 101 is removed prior to a subsequent masking andbulk crystal growth operation, for example, by sawing, lapping,grinding, and/or etching.

FIGS. 4A, 4B, and 4C are simplified diagrams illustrating a method offorming a free-standing group III metal nitride boule and free-standinggroup III metal nitride wafers. In certain embodiments, substrate 101 isremoved from ammonothermal group III metal nitride layer 213 (FIG. 4A,which is similarly configured as FIG. 3E), or the last such layerdeposited, to form a free-standing, merged ammonothermal group III metalnitride boule 413, which comprises at least a portion of theammonothermal group III metal nitride layer 213. Removal of substrates101 may be accomplished by one or more of sawing, grinding, lapping,polishing, laser lift-off, self-separation, and etching to form aprocessed free-standing laterally-grown group III metal nitride boule413. The processed free-standing laterally-grown group III metal nitrideboule 413 may include a similar or essentially identical composition asthe ammonothermal group III metal nitride layer and etching may beperformed under conditions where the etch rate of the back side ofsubstrate 101 is much faster than the etch rate of the front surface ofthe ammonothermal group III metal nitride layer. In certain embodimentsa portion of ammonothermal group III metal nitride layer 213, or thelast such layer deposited, may be protected from attack by the etchantby deposition of a mask layer, wrapping the portion of the layer withTeflon, clamping the portion of the layer against Teflon, painting withTeflon paint, or the like. In a specific embodiment, substrate 101comprises single crystal gallium nitride, large-area surface 102 ofsubstrate 101 has a crystallographic orientation within about 5 degreesof a (0001) crystallographic orientation, and substrate 101 ispreferentially etched by heating in a solution comprising one or more ofH₃PO₄, H₃PO₄ that has been conditioned by prolonged heat treatment toform polyphosphoric acid, and H₂SO₄ at a temperature between about 150degrees Celsius and about 500 degrees Celsius for a time between about30 minutes and about 5 hours, or by heating in a molten flux comprisingone or more of NaOH and KOH. Surprisingly, patterned mask layer(s) 111may facilitate preferential removal of substrate 101 by acting as anetch stop. The processed free-standing, merged ammonothermal group IIImetal nitride boule 413 may include one or more window regions 415 thatwere formed above exposed regions 120, such as openings 112 in patternedmask layer(s) 111, on a substrate 101. The processed free-standing,merged laterally-grown group III metal nitride boule 413 may alsoinclude one or more wing regions 417 that were formed above non-openregions in patterned mask layer(s) 111, and a pattern oflocally-approximately-linear arrays 419 of threading dislocations, asshown in FIG. 4B, and one or more second coalescence fronts 435. One ormore of front surface 421 and back surface 423 of free-standing, mergedammonothermal group III metal nitride boule 413 may be lapped, polished,etched, and chemical-mechanically polished. As similarly discussedabove, the pattern of locally-approximately-linear arrays 419 and one ormore second coalescence fronts 435 may include a coalescence frontregion that includes a “sharp boundary” that has a width less than about25 micrometers or less than about 10 micrometers that is disposedbetween the adjacent wing regions 417, or an “extended boundary” thathas a width between about 25 micrometers and about 1000 micrometers orbetween about 30 micrometers and about 250 micrometers that is disposedbetween the adjacent wing regions 417, depending on the growthconditions.

In certain embodiments, the edge of free-standing, merged ammonothermalgroup III metal nitride boule 413 is ground to form acylindrically-shaped ammonothermal group III metal nitride boule. Incertain embodiments, one or more flats is ground into the side offree-standing, merged ammonothermal group III metal nitride boule 413.In certain embodiments, free-standing, merged ammonothermal group IIImetal nitride boule 413 is sliced into one or more free-standing, mergedammonothermal group III metal nitride wafers 431, as shown in FIG. 4C.The slicing may be performed by multi-wire sawing, multi-wire slurrysawing, slicing, inner-diameter sawing, outer-diameter sawing, cleaving,ion implantation followed by exfoliation, spalling, laser cutting, orthe like. One or more large-area surface of free-standing, mergedammonothermal group III metal nitride wafers 431 may be lapped,polished, etched, electrochemically polished, photoelectrochemicallypolished, reactive-ion-etched, and/or chemical-mechanically polishedaccording to methods that are known in the art. In certain embodiments,a chamfer, bevel, or rounded edge is ground into the edges offree-standing, merged ammonothermal group III metal nitride wafers 431.The free-standing, merged ammonothermal group III metal nitride wafersmay have a diameter of at least about 10 millimeters, at least about 25millimeters, at least about 50 millimeters, at least about 75millimeters, at least about 100 millimeters, at least about 150millimeters, at least about 200 millimeters, at least about 300millimeters, at least about 400 millimeters, or at least about 600millimeters and may have a thickness between about 50 micrometers andabout 20 millimeters or between about 150 micrometers and about 5millimeter. One or more large-area surface of free-standing, mergedammonothermal group III metal nitride wafers 431 may be used as asubstrate for group III metal nitride growth by chemical vapordeposition, metalorganic chemical vapor deposition, hydride vapor phaseepitaxy, molecular beam epitaxy, flux growth, solution growth,ammonothermal growth, among others, or the like.

Tiled Seed Crystal Array Configuration Examples

In some embodiments of the disclosure, the tiled array of seed crystalsused during a crystal growth process, or one or more steps in a multiplestep crystal growth process, may include the use of and alignment ofseed crystals that have desirable crystallographic and structuralattributes, such that the crystal layers grown from the formed tiledseed crystal array have a reduced number of crystalline defects,particularly at coalescence fronts, and reduced misalignment betweenadjacent grains or seed crystals. In certain embodiments, an array ofseed crystals 370 are aligned, oriented and positioned in aone-dimensional array, as illustrated in FIGS. 20B-20C, rather than in atwo-dimensional array, as shown in FIGS. 17A-19G. Tiling in onedimension at a time may offer certain advantages, relative to tilingsimultaneously in two dimensions, as described in more detail below. Ingeneral, a fixture or handle substrate supporting the two or more seedcrystals that are positioned in an array is approximately CTE-matched tothe seed crystals. However, in the case of tiling of nonpolar orsemipolar GaN crystals, where the CTEs in the c- and a-directions aredistinct, by virtue of the wurtzite crystal structure, the handlesubstrate is unlikely to be CTE-matched in both directions unless thehandle substrate is also single-crystal GaN having the samecrystallographic orientation. An advantage of forming and coalescing aone-dimensional array of seed crystals is that it can be more difficultto coalesce crystals in two directions simultaneously than to do so onlyin one growth direction at a time. In addition, the defect level at thecoalescence boundaries and the tile-to-tile misorientation angle arecritically dependent on the accuracy of the polishing and alignmentoperations, and thus it may be easier to align and configure aone-dimensional array of seed crystals such that a very high quality,coalesced GaN crystal can be formed in subsequent operations.

In certain embodiments of the disclosure, a plurality of first GaN tileor seed crystals 2001 are provided for tiling in a first direction toform a one-dimensional array of seed crystals, as shown in FIGS.20A-20C. In certain embodiments, each of the tile crystals 2001, whichmay include or consist of a seed crystal 370, is prepared from a commonsingle crystal, for example, by multi-wire-sawing, grinding, polishing,and chemical-mechanical polishing. The formed tile crystals 2001 may betiled in one dimension, for example, along the c-direction for m-planeseed crystals, coalesced, and grown out to an approximately equilibriumshape, as shown in FIG. 20A-20E. In another specific embodiment, c-planeseed crystals may be tiled along an a-direction and grown out to anapproximately equilibrium shape. The original seed may have been grownammonothermally or by HVPE.

During the process of forming the one-dimensional array of seedcrystals, after positioning and aligning the seed crystals in a desiredorientation, a coalescence step is used to couple the seed crystalsdisposed in the one-dimensional array together (Y direction). During thecoalescence process, gaps 2011 between adjacent tile crystals 2001 (FIG.20B, analogous to gaps 1711 in FIGS. 17A-17F) may fill in, formingcoalescence fronts 2015 in the same positions as gaps 2011 (FIGS. 20Band 20D) The coalescence step may be carried out in a separate step, forexample, using a mechanical fixture as shown in FIGS. 18A-18D, bybonding using a polycrystalline group III nitride layer, as shown inFIGS. 19A-19C, or by bonding to a handle substrate, as described below.The coalesced array of seed crystals may then be removed from the handlesubstrate, and used as a seed for a subsequent ammonothermal crystalgrowth run. In the subsequent ammonothermal crystal growth process thegrown crystal layer 2045 formed on the coalesced array of seed crystalscan be grown out to a near-equilibrium shape to form a grown tiled seedcrystal 2050, as illustrated in FIGS. 20D-20E.

In some embodiments, rather than using a mechanical fixture (FIGS.18A-18D) or polycrystalline group III nitride bonding layer (FIGS.19A-19C), the coalescence step is performed using a handle substratethat consists of or includes a supporting component that is formed fromone or more of molybdenum, a molybdenum alloy, a single crystal orpolycrystalline group III metal nitride, or another material that has aclose CTE match to the seed crystals and is compatible with the crystalgrowth environment. An adhesion layer may be deposited on the front sideof the handle substrate and the back side of the seed crystals. Theadhesion layer may include one or more of SiO₂, GeO₂, SiN_(x), AlNx, orB, Al, Si, P, Zn, Ga, Si, Ge, Au, Ag, Ni, Ti, Cr, Zn, Cd, In, Sn, Sb,Tl, W, In, Cu, or Pb, or an oxide, nitride, or oxynitride thereof. Incertain embodiments, the composition of the adhesion layer on at leastone of the handle substrate and the seed crystals may have a meltingpoint may be chosen so as to undergo nascent melting at a temperaturebelow about 300 degrees Celsius, below about 400 degrees Celsius, orbelow about 500 degrees Celsius. In certain embodiments, the compositionof the adhesion layer on the other of the at least one of the handlesubstrate and the seed crystals may have a melting point may be chosenso as to undergo nascent melting at a temperature below about 300degrees Celsius, below about 400 degrees Celsius, or below about 500degrees Celsius, and may be chosen so as to have a melting point aboveabout 600 degrees Celsius, above about 700 degrees Celsius, above about800 degrees Celsius, or above about 900 degrees Celsius. The compositionand structure of the adhesion layer may be chosen so as to undergonascent melting at a temperature below about 300 degrees Celsius, belowabout 400 degrees Celsius, below about 500 degrees Celsius, or belowabout 600 degrees Celsius, then, following bonding to a mating adhesionlayer and a thermal treatment at a temperature below the solidustemperature, to remain unmelted, or with a volume fraction of melt belowabout 20%, below about 10%, or below about 5%, at a temperature aboveabout 600 degrees Celsius, above about 700 degrees Celsius, above about800 degrees Celsius, or above about 900 degrees Celsius. The seedcrystals may be bonded to the handle substrate at a first temperature,at which at least one adhesion layer composition may be molten, thenheat treated so as to remain unmelted at a second, higher temperature,at which a crystal growth process is performed to cause coalescence ofthe seed crystals into a merged crystal. Further details are describedin U.S. Pat. No. 10,400,352, which is hereby incorporated by referencein its entirety.

In some embodiments of the crystal forming process, the grown tiled seedcrystal 2050 is then sliced, as shown schematically in FIG. 21A. In oneexample, the slicing is performed parallel to an m-plane and parallel tothe original seed surface, forming long, narrow portions of the growntiled seed crystal 2050, for example, crystals 2101, 2102, 2103, 2104,2105, 2106, 2107, and 2108. The long, narrow portions of the grown tiledseed crystal 2050 are then tiled side-by-side, as shown in FIG. 21B.Since adjacent strips were formed from crystals above or below oneanother, the crystallographic orientation along a row will be quiteprecise, for example, better than 0.3°, better than 0.1°, better than0.05°, better than 0.02°, or better than 0.01°, even if the originalone-dimensional tiling process shown in FIGS. 20A-20E was not nearly asaccurate.

During the process of forming the array of seed crystals, illustrated inFIGS. 21B-21C, after positioning and aligning the narrow portions of thegrown tiled seed crystal in a desired orientation, a coalescence step isused to couple the narrow portions of the grown tiled seed crystaltogether (X direction). During the coalescence process, gaps 2112between adjacent tile crystals 2001 (FIG. 21B) may fill in, formingcoalescence fronts 2115 in the same positions as gaps 2112 (FIGS. 21Band 21D). After coalescence, a first second-dimension-tiled crystal maybe de-bonded from a fixture or handle substrate and re-grown to anear-equilibrium shape, encompassing regrown crystal layer 2145, asshown in FIGS. 21D-21E. The regrown crystal 2150 will include a growncrystal layer 2145 that includes coalescence fronts 2115 formed withinor over gaps 2112 (FIG. 21B) found in the array of crystals, which aresimilar to the second coalescence fronts 435 described above, along withcoalescence fronts 2015 formed by extension of pre-existing coalescencefronts 2015 in seed crystals 2101, 2102, etc. Inaccuracies in theoriginal tiling may be manifested as grain boundaries in the Y, or axialdirection (i.e., coalescence fronts 2015; c-direction in the specificexample shown) but misorientation in the X-direction (i.e., coalescencefronts 2115; a-direction in the specific example shown) should beminimal.

The regrown crystal 2150 may then be sliced in the X-Y plane (parallelto the m-plane in the specific example shown), as shown schematically inFIG. 22A, forming, for example, slices 2201, 2202, 2203, 2204, 2205,2206, 2207, and 2208. In addition, as shown in FIG. 22B, the regrowncrystal 2150 or slices 2201-2208 may then be sliced at positions 2220,corresponding to the defective grain boundaries found at the coalescencefronts 2015, which are parallel to c-plane in the specific example shown(FIG. 21D) forming, for examples slabs 2201A, 2201B, 2201C, . . . ,2202A, 2202B, 2202C, . . . 2208C, 2208D, and 2208E (e.g., 40 totalslabs). After forming the slices 2201-2208 and sectioning the slices atpositions 2220, the resulting slabs 2201A-2208E can then be tiled again,in a direction orthogonal to the previous tiling operation, as shown inFIG. 22C. In this configuration, slabs that are adjacent to one anotherin the Z direction are placed side-by-side to make a one-dimensionalarray in the Y direction, with edges prepared at the positions 2220placed next to one another. This formed array of slabs 2201A-2208A(FIGS. 22C-22D) will allow the very small misorientations found in theregrown crystal 2150 to be replicated in the subsequently formed entiremosaic crystal 2250.

During the process of forming the array of slabs 2201A-2208A,illustrated in FIGS. 22B-22C, after positioning and aligning the slabs2201A-2208A in a desired orientation, a coalescence step is used tocouple the array of slabs 2201A-2208A together (Y direction). During thecoalescence process, gaps 2212 between adjacent slabs 2201A-2208A (FIG.22C) may fill in, forming coalescence fronts 2215 in the same positionsas gaps 2212 (FIGS. 22C and 22E). Each of the slabs 2201A-2208A disposedin the array are coupled together by at least one coalescence front 2215(FIG. 22C). Once the array of slabs 2201A-2208A are re-coalesced theycan then be de-bonded from a fixture or handle substrate, and re-grownto form an equilibrium shape having a grown crystal layer 2245 thatincludes a greatly reduced defect concentration associated with thecoalescence fronts 2215, as shown in FIG. 22E. Similar procedures may befollowed to coalesce and grow on slabs 2201B-2208B, 2201C-2208C, . . .and 2201E-2208E.

The procedure shown schematically in FIGS. 20A-22F may be employed tofabricate large-area, low-defect m-plane GaN crystals suitable for useas seeds in subsequent ammonothermal crystal growth of m-plane boules orin subsequent bulk crystal growth by another method, such as HVPE orflux growth. Similar, sequential 1-D tiling operations may be used toprepare large-area, low-defect c-plane or semipolar GaN crystalssuitable for use as seeds in subsequent bulk crystal growth or for useas substrates for electronic or optoelectronic device fabrication.

In certain embodiments, the mosaic crystal 2250 is sliced along a shortdimension or at an oblique angle, for example, to form seed crystalssuitable for use as seeds in subsequent ammonothermal crystal growth orin subsequent bulk crystal growth by another method, such as HVPE orflux growth, for use in a further one-dimensional or two-dimensionaltiling process, or for use as substrates for electronic oroptoelectronic device fabrication.

In an alternative embodiment, for example, for growth of c-plane orsemipolar crystals, the initial one-dimensional tiling operation (FIG.20A-20D) is omitted, and isolated m-plane crystals are simply grown to anear-equilibrium shape. The formed crystals may be sliced parallel tom-plane and tiled as shown in FIGS. 21A-21E to form the regrown crystal2150. Alternatively, the formed crystals may be sliced parallel toc-plane or in a semipolar orientation to prepare seeds for aone-dimensional tiling operation. Crystals sliced from the region of theboule that grew in the +c [0001] direction have a substantially-reduceddislocation density and are particularly well-suited for growth ofc-plane and/or semipolar crystals with a dislocation density below 10⁶cm⁻², below 10⁵ cm⁻², below 10⁴ cm⁻², or below 10³ cm⁻².

Relative to a two-dimensional tile-in-one-step process, as illustratedschematically in FIGS. 17A-19F, the sequential 1-D tiling approach mayhave several advantages, including enabling easier tile selection,preparation, and stacking; more accurately aligned single crystaldomains; reduced CTE mismatch to a handle substrate or fixture andthereby reduced risk of cracking; and reduced risk of individual tilesbeing m is-oriented beyond a target specification, for example, 0.1°.

Grown and Freestanding Crystal Examples

FIGS. 5A-5E are simplified diagrams illustrating threading dislocationpatterns formed above individual tile crystals that have been formed bythe patterned growth methods summarized in FIGS. 1A-4C. The individualtile crystals illustrated in FIGS. 5A-5E, can form part of afree-standing, merged group III metal nitride boule 413 or wafer 431,which are described in relation to FIGS. 4A-4C, or form part of thefree-standing, merged ammonothermal group III nitride boule or wafer,which are illustrated in FIGS. 6A-6G, which are described further below.The large-area surfaces of the free-standing, merged ammonothermal groupIII metal nitride boule 413 or wafers 431 may be characterized by apattern of locally-approximately-linear arrays 419 of threadingdislocations that propagated from first coalescence fronts 219 formedduring the epitaxial lateral overgrowth process, as discussed above inconjunction with FIGS. 3A-3E. The pattern oflocally-approximately-linear arrays of threading dislocations may be 2Dhexagonal, square, rectangular, trapezoidal, triangular, 1D linear, oran irregular pattern that is formed at least partially due to thepattern of the exposed regions 120 (FIGS. 1F-1L) used during the processto form free-standing laterally-grown group III metal nitride boule 413.One or more window regions 415 are formed above the exposed regions 120(FIGS. 1F-1L), and one or more wing regions 417 are formed on portionsthat are not above the exposed regions 120, that is, were formed bylateral growth. As discussed above, the formed first coalescence fronts219 or pattern of locally-approximately-linear arrays 419 may includecoalescence front regions that have a lateral width (i.e., measuredparallel to the surface of the page containing FIGS. 5A-5E) that canvary depending on the growth conditions.

More complex patterns are also possible and may be advantageous, forexample, in being more resistant to cracking or cleaving. The pattern502 may be elongated in one direction compared to another orthogonaldirection, for example, due to the free-standing, merged laterally-growngroup III metal nitride boule 413 being sliced at an inclined anglerelative to the large-area surface of a free-standing, mergedammonothermal group III metal nitride boule 413. The pattern 502 oflocally-approximately-linear arrays of threading dislocations may becharacterized by a linear array of threading dislocations (FIG. 5D) thathave a pitch dimension L between about 5 micrometers and about 20millimeters or between about 200 micrometers and about 5 millimeters.The pattern 502 of locally-approximately-linear arrays of threadingdislocations may be characterized by a pitch dimension L (FIGS. 5A, 5B),or by pitch dimensions L₁ and L₂ in two orthogonal directions (FIGS. 5Cand 5E), between about 5 micrometers and about 20 millimeters or betweenabout 200 micrometers and about 5 millimeters, or between about 500micrometers and about 2 millimeters. In certain embodiments, the pattern502 of locally-approximately-linear arrays of threading dislocations isapproximately aligned with the underlying crystal structure of the groupIII metal nitride, for example, with the locally-approximately-lineararrays lying within about 5 degrees, within about 2 degrees, or withinabout 1 degree of one or more of <1 0 −1 0>, <1 1 −2 0>, or [0 0 0 ±1]or their projections in the plane of the surface of the free-standing,merged ammonothermal group III metal nitride boule 413 or group IIImetal nitride wafer 431. The linear concentration of threadingdislocations in the pattern may be less than about 1×10⁵ cm⁻¹, less thanabout 3×10⁴ cm⁻¹, less than about 1×10⁴ cm⁻¹, less than about 3×10³cm⁻¹, less than about 1×10³ cm⁻¹, less than about 3×10² cm⁻¹, or lessthan about 1×10² cm⁻¹. The linear concentration of threadingdislocations in the pattern 502 may be greater than 5 cm⁻¹, greater than10 cm⁻¹, greater than 20 cm⁻¹, greater than 50 cm⁻¹, greater than 100cm⁻¹, greater than 200 cm⁻¹, or greater than 500 cm⁻¹.

Referring again to FIGS. 5A-5E, the large-area surfaces of individualgrains or domains within the free-standing, merged ammonothermal groupIII metal nitride boule or wafer may further be characterized by anarray of wing regions 417 and by an array of window regions 415. Eachdomain, or sometimes referred to herein as a grain, may be formed bygrowth above an individual tile crystal (e.g., seed crystals 370). Adomain will generally include wing regions, window regions, coalescencefronts and locally-approximately-linear arrays of dislocations and aregenerally bounded by coalescence fronts. Each wing region 417 may bepositioned between adjacent locally-approximately-linear arrays 419 ofthreading dislocations. Each window region 415 may be positioned withina single wing region 417 or may be positioned between two adjacent wingregions 417 and may have a minimum dimension between 10 micrometers and500 micrometers and be characterized by concentration of threadingdislocations between 10³ cm⁻² and 10⁸ cm⁻², resulting from residualthreading dislocations that propagated vertically from window regionsduring the bulk crystal growth process, and by a concentration ofstacking faults below 10³ cm⁻¹. In some embodiments the boundary betweenthe window regions and the wing regions may be decorated withdislocations, for example, with a line density between about 5 cm⁻¹ and10⁵ cm⁻¹.

The arrays may be elongated in one direction compared to anotherorthogonal direction, for example, due to the boule being sliced at aninclined angle relative to the large-area surface of a free-standing,merged ammonothermal group III metal nitride boule. The pattern oflocally-approximately-linear arrays 419 of threading dislocations may becharacterized by a pitch dimension L, or by pitch dimensions L₁ and L₂in two orthogonal directions, between about 5 micrometers and about 20millimeters or between about 200 micrometers and about 2 millimeters. Incertain embodiments, the first pattern of locally-approximately-lineararrays 419 of threading dislocations is approximately aligned with theunderlying crystal structure of the group III metal nitride, forexample, with the locally-approximately-linear arrays lying within about5 degrees, within about 2 degrees, or within about 1 degree of one ormore of <1 0 −1 0>, <1 1 −2 0>, or [0 0 0 ±1] or their projections inthe plane of the surface of the free-standing ammonothermal group IIInitride boule or wafer. The linear concentration of threadingdislocations in the pattern may be less than about 1×10⁵ cm⁻¹, less thanabout 3×10⁴ cm⁻¹, less than about 1×10⁴ cm⁻¹, less than about 3×10³cm⁻¹, less than about 1×10³ cm⁻¹, less than about 3×10² cm⁻¹, or lessthan about 1×10² cm⁻¹. The linear concentration of threadingdislocations in the pattern may be greater than 5 cm⁻¹, greater than 10cm⁻¹, greater than 20 cm⁻¹, greater than 50 cm⁻¹, greater than 100 cm⁻¹,greater than 200 cm⁻¹, or greater than 500 cm⁻¹.

The concentration of threading dislocations in the wing regions 417between the locally-approximately-linear arrays of threadingdislocations may be below about 10⁵ cm⁻², below about 10⁴ cm⁻², belowabout 10³ cm⁻², below about 10² cm⁻¹, or below about 10 cm⁻². Theconcentration of threading dislocations in the surface of the windowregions 415 may be less than about 10⁸ cm⁻², less than about 10⁷ cm⁻²,less than about 10⁶ cm⁻², less than about 10⁵ cm⁻², or less than about10⁴ cm⁻². The concentration of threading dislocations in the surface ofthe window regions may be higher than the concentration of threadingdislocations in the surface of the wing regions by at least a factor oftwo, by at least a factor of three, by at least a factor of ten, by atleast a factor of 30, or by at least a factor of 100. The concentrationof threading dislocations in the surface of the window regions may behigher than concentration of threading dislocations in the surface ofthe wing regions by less than a factor of 10⁴, by less than a factor of3000, by less than a factor of 1000, by less than a factor of 300, byless than a factor of 100, or by less than a factor of 30. In someembodiments the boundary between the window regions 415 and the wingregions 417 may be decorated with dislocations, for example, with a linedensity between about 5 cm⁻¹ and 10⁵ cm⁻¹. The concentration ofthreading dislocations, averaged over a large area surface of thefree-standing ammonothermal group III nitride boule or wafer, may bebelow about 10⁷ cm⁻², below about 10⁶ cm⁻², below about 10⁵ cm⁻², belowabout 10⁴ cm⁻², below about 10³ cm⁻², or below about 10² cm⁻². Theconcentration of stacking faults, averaged over a large area surface ofthe free-standing ammonothermal group III nitride boule or wafer, may bebelow about 10³ cm⁻¹, below about 10² cm⁻¹, below about 10 cm⁻¹, belowabout 1 cm⁻¹, or below about 0.1 cm⁻¹, or may be undetectable. In someembodiments, for example, after repeated re-growth on a seed crystalwith a patterned array of dislocations and/or growth to a thicknessgreater than 2 millimeters, greater than 3 millimeters, greater than 5millimeters, or greater than 10 millimeters, the positions of thethreading dislocations may be displaced laterally to some extent withrespect to the pattern on the seed crystal. In such a case the regionswith a higher concentration of threading dislocations may be somewhatmore diffuse than the relatively sharp lines illustrated schematicallyin FIGS. 5A-5E. However, the concentration of threading dislocations asa function of lateral position along a line on the surface will varyperiodically, with a period between about 5 micrometers and about 20millimeters or between about 200 micrometers and about 5 millimeters.The concentration of threading dislocations within theperiodically-varying region may vary by at least a factor of two, atleast a factor of 5, at least a factor of 10, at least a factor of 30,at least a factor of 100, at least a factor of 300, or at least a factorof 1000.

Referring to FIGS. 6A-6F, as discussed above, a free-standing, mergedammonothermal group III nitride boule or wafer can be formed by use ofone or more of the tiling processes described in relation to FIGS. 3A-4Cand 17A-22F. The free-standing, merged ammonothermal group III nitrideboule or wafer can include two or more domains or grains separated byone or more second lines of dislocations 635, the latter originatingfrom the second coalescence fronts 235 or 2215 formed during lateralgrowth of ammonothermal group III metal nitride material from one seedto its neighbor, as shown schematically in FIGS. 2C, 3E, and 22E.Depending on the geometry of the original nitride crystals, the patternof domains may be, for example, (a) square (FIGS. 6A and 17A), (b)rectangular (FIGS. 6B and 17B), (c) hexagonal (FIGS. 6C and 17C), (d)rhombohedral (FIGS. 6D and 17D), (e) a mix of hexagonal and pentagonal(FIGS. 6E and 17E); or (f) a mix of hexagonal and rhombohedral (FIGS. 6Fand 17F). Other patterns are also possible. FIG. 6G illustrates anexample of a square free-standing, merged ammonothermal group IIInitride boule or wafer that was formed using a plurality of tiled seedcrystals (e.g., seed crystals 370), which are shown in FIG. 1G, during acrystal growth process, where each of the domains resulting from asingle tile crystal (e.g., seed crystal 370) includes window and wingregions and coalescence fronts. The domains may have a first lateraltile dimension 680 and a second lateral tile dimension 690,corresponding approximately to original tile crystal dimensions 380 and390, respectively (see FIGS. 17A-17F), the lateral dimensions defining aplane that is perpendicular to the thickness, where each of the firstlateral tile dimension 680 and the second lateral tile dimension 690 maybe at least about 5 millimeters, 10 millimeters, 15 millimeters, 20millimeters, 25 millimeters, 35 millimeters, 50 millimeters, 75millimeters, 100 millimeters, 150 millimeters, or at least about 200millimeters. The polar misorientation angle γ between adjacent domainsmay be less than 0.5 degree, less than 0.2 degree, less than 0.1 degree,less than 0.05 degree, less than 0.02 degree, or less than 0.01 degree.The first lateral tile dimension 680 may be approximately the same asthe first lateral seed dimension (i.e., X-direction dimension 380).Similar, the second lateral tile dimension 690 may be approximatelyequal to the second lateral seed dimension (i.e., Y-direction dimension390). The misorientation angles α and β between adjacent domains may beless than 0.5 degree, less than 0.2 degree, less than 0.1 degree, lessthan 0.05 degree, less than 0.02 degree, or less than 0.01 degree.Typically, γ will be less than or equal to α and β. The crystallographicmisorientation angles α, β, and γ may be greater than about 0.01 degree,greater than about 0.02 degree, greater than about 0.05 degree, orgreater than about 0.1 degree. The density of dislocations along thelines between adjacent domains may be less than about 5×10⁵ cm⁻¹, lessthan about 2×10⁵ cm⁻¹, less than about 1×10⁵ cm⁻¹, less than about 5×10⁴cm⁻¹, less than about 2×10⁴ cm⁻¹, less than about 1×10³ cm⁻¹, less thanabout 5×10³ cm⁻¹, less than about 2×10³ cm⁻¹, or less than about 1×10³cm⁻¹. The density of dislocations along the lines between adjacentdomains may be greater than 50 cm⁻¹, greater than 100 cm⁻¹, greater than200 cm⁻¹, greater than 500 cm⁻¹, greater than 1,000 cm⁻¹, greater than2000 cm⁻¹, or greater than 5000 cm⁻¹.

The free-standing, merged ammonothermal group III nitride boule or wafermay have a symmetric x-ray rocking curve, for example, (002) in the caseof c-plane, full width at half maximum (FWHM) less than about 300 arcsec, less than about 200 arc sec, less than about 100 arc sec, less thanabout 50 arc sec, less than about 35 arc sec, less than about 25 arcsec, or less than about 15 arc sec. The free-standing, mergedammonothermal group III nitride boule or wafer may have a non-symmetricx-ray rocking curve, for example, (201) or (102) in the case of c-plane,full width at half maximum (FWHM) less than about 300 arc sec, less thanabout 200 arc sec, less than about 100 arc sec, less than about 50 arcsec, less than about 35 arc sec, less than about 25 arc sec, or lessthan about 15 arc sec. The free-standing, merged ammonothermal group IIInitride boule or wafer may have a thickness between about 100 micronsand about 100 millimeters, or between about 1 millimeter and about 10millimeters. The free-standing, merged ammonothermal group III nitrideboule or wafer may have a diameter of at least about 15 millimeters, atleast about 20 millimeters, at least about 25 millimeters, at leastabout 35 millimeters, at least about 50 millimeters, at least about 75millimeters, at least about 100 millimeters, at least about 150millimeters, at least about 200 millimeters, or at least about 400millimeters. The surface of the free-standing, merged ammonothermalgroup III nitride boule or wafer may have a crystallographic orientationwithin 10 degrees, within 5 degrees, within 2 degrees, within 1 degree,within 0.5 degree, within 0.2 degree, within 0.1 degree, within 0.05degree, within 0.02 degree, or within 0.01 degree of (0 0 0 1) Ga-polar,(0 0 0 −1) N-polar, {1 0 −1 0} non-polar, or {1 1 −2 0} non-polara-plane. The surface of the free-standing, merged ammonothermal groupIII nitride boule or wafer may have a (h k i l) semi-polar orientation,where i=−(h+k) and l and at least one of h and k are nonzero. In aspecific embodiment, the crystallographic orientation of thefree-standing, merged ammonothermal group III nitride boule or wafer iswithin 10 degrees, within 5 degrees, within 2 degrees, within 1 degree,within 0.5 degree, within 0.2 degree, within 0.1 degree, within 0.05degree, within 0.02 degree, or within 0.01 degree of {1 1 −2 ±2}, {6 0-6±1}, {5 0 −5 ±1}, {40 −4 ±1}, {3 0 −3 ±1}, {5 0 −5 ±2}, {7 0 −7 ±3}, {20 −2 ±1}, {3 0 −3 ±2}, {4 0 −4 ±3}, {5 0 −5 ±4}, {1 0 −1 ±1}, {1 0 −1±2}, {1 0 −1 ±3}, {2 1 −3 ±1}, or {3 0 −3 ±4}. The free-standing, mergedammonothermal group III nitride boule or wafer has a minimum lateraldimension of at least ten millimeters. In some embodiments, the mergednitride crystal has a minimum lateral dimension of at least twocentimeters, at least three centimeters, at least four centimeters, atleast five centimeters, at least six centimeters, at least eightcentimeters, at least ten centimeters, or at least twenty centimeters.

In some embodiments, the free-standing, merged ammonothermal group IIInitride boule or wafer is used as a substrate for epitaxy, forming asemiconductor structure. The free-standing, merged ammonothermal groupIII nitride boule may be sawed, lapped, polished, dry etched, and/orchemical-mechanically polished by methods that are known in the art. Oneor more edges of the free-standing, merged ammonothermal group IIInitride boule or wafer may be ground. The free-standing, mergedammonothermal group III nitride boule or wafer may be placed in asuitable reactor and an epitaxial layer grown by MOCVD, MBE, HVPE, orthe like. In a particular embodiment, the epitaxial layer comprises GaNor Al_(x)In_(y)Ga_((1-x-y))N, where 0≤x, y≤1. The morphology of theepitaxial layer is uniform from one domain to another over the surfacebecause the surface orientation is almost identical.

In some embodiments, the free-standing, merged ammonothermal group IIInitride boule or wafer is used as a substrate for further tiling. Forexample, referring to FIGS. 17A through 19D, the seed crystals 370themselves may be chosen to be a free-standing, merged ammonothermalgroup III metal nitride boule or wafer. The tiling, coalescence, andre-tiling operation may be iterated more than twice, more than 4 times,more than 8 times, or more than 16 times. In this way, by successivetiling operations, a merged nitride crystal with excellent crystallinequality and very large diameter may be fabricated.

The free-standing, merged ammonothermal group III nitride boule or wafermay be used as a substrate for fabrication into optoelectronic andelectronic devices such as at least one of a light emitting diode, alaser diode, a photodetector, an avalanche photodiode, a transistor, arectifier, a Schottky rectifier, a thyristor, a p-i-n diode, ametal-semiconductor-metal diode, high-electron-mobility transistor, ametal semiconductor field effect transistor, a metal oxide field effecttransistor, a power metal oxide semiconductor field effect transistor, apower metal insulator semiconductor field effect transistor, a bipolarjunction transistor, a metal insulator field effect transistor, aheterojunction bipolar transistor, a power insulated gate bipolartransistor, a power vertical junction field effect transistor, a cascodeswitch, an inner sub-band emitter, a quantum well infraredphotodetector, a quantum dot infrared photodetector, a solar cell, or adiode for photoelectrochemical water splitting and hydrogen generationdevice. In some embodiments, the positions of the devices with respectto the domain structure in the free-standing, merged ammonothermal groupIII nitride boule or wafer are chosen so that the active regions ofindividual devices lie within a single domain or grain of thefree-standing, merged ammonothermal group III nitride boule or wafer.

The free-standing, merged ammonothermal group III metal nitride boule orwafer may have a large-area crystallographic orientation within 5degrees, within 2 degrees, within 1 degree, within 0.5 degree, within0.2 degree, within 0.1 degree, within 0.05 degree, within 0.02 degree,or within 0.01 degree of (0001) +c-plane, (000-1) −c-plane, {10-10}m-plane, {1 1 −2 0} a-plane, {11-2±2}, {60-6±1}, {50-5±1}, {40-4±1},{30-3±1}, {50-5±2}, {70-7±3}, {20-2±1}, {30-3±2}, {40-4±3}, {50-5±4},{10-1±1}, {1 0 −1 ±2}, {1 0 −1 ±3}, {2 1 −3 ±1}, or {3 0 −3 ±4}. Thefree-standing ammonothermal group III metal nitride boule or wafer mayhave an (h k i l) semipolar large-area surface orientation, wherei=−(h+k) and l and at least one of h and k are nonzero.

In certain embodiments, a large-area surface of a free-standingammonothermal group III metal nitride crystal or wafer has acrystallographic orientation that is miscut from {10-10} m-plane bybetween about −60 degrees and about +60 degrees toward [0001]+c-direction and by up to about 10 degrees toward an orthogonal <1−210>a-direction. In certain embodiments, a large-area surface of thefree-standing ammonothermal group III metal nitride crystal or wafer hasa crystallographic orientation that is miscut from {10-10} m-plane bybetween about −30 degrees and about +30 degrees toward [0001]+c-direction and by up to about 5 degrees toward an orthogonal <1−210>a-direction. In certain embodiments, a large-area surface of thefree-standing ammonothermal group III metal nitride crystal or wafer hasa crystallographic orientation that is miscut from {10-10} m-plane bybetween about −5 degrees and about +5 degrees toward [0001] +c-directionand by up to about 1 degree toward an orthogonal <1−210> a-direction.The free-standing ammonothermal group III metal nitride crystal or wafermay have a stacking fault concentration below 10² cm⁻¹, below 10 cm⁻¹,or below 1 cm⁻¹, and a very low dislocation density, below about 10⁵cm⁻², below about 10⁴ cm⁻², below about 10³ cm⁻², below about 10² cm⁻²,or below about 10 cm⁻² on one or both of the two large area surfaces.

The free-standing, merged ammonothermal group III metal nitride boule orwafer may have a symmetric x-ray rocking curve full width at halfmaximum (FWHM) less than about 200 arcsec, less than about 100 arcsec,less than about 50 arcsec, less than about 35 arcsec, less than about 25arcsec, or less than about 15 arcsec. The free-standing, mergedammonothermal group III metal nitride boule or wafer may have acrystallographic radius of curvature greater than 0.1 meter, greaterthan 1 meter, greater than 10 meters, greater than 100 meters, orgreater than 1000 meters, in at least one, at least two, or in threeindependent or orthogonal directions.

In certain embodiments, at least one surface of the free-standing,merged ammonothermal group III metal nitride boule or wafer has atomicimpurity concentrations of at least one of oxygen (O), and hydrogen (H)above about 1×10¹⁶ cm⁻³, above about 1×10¹⁷ cm⁻³, or above about 1×10¹⁸cm⁻³. In certain embodiments, a ratio of the atomic impurityconcentration of H to the atomic impurity concentration of 0 is betweenabout 0.3 and about 1000, between about 0.4 and about 10, or betweenabout 10 and about 100. In certain embodiments, at least one surface ofthe free-standing, merged ammonothermal group III metal nitride boule orwafer has impurity concentrations of at least one of lithium (L₁),sodium (Na), potassium (K), fluorine (F), chlorine (Cl), bromine (Br),or iodine (I) above about 1×10¹⁵ cm⁻³, above about 1×10¹⁶ cm⁻³, or aboveabout 1×10¹⁷ cm⁻³, above about 1×10¹⁸ cm⁻³. In certain embodiments, thetop and bottom surfaces of the free-standing, merged ammonothermal groupIII metal nitride boule or wafer may have impurity concentrations of O,H, carbon (C), Na, and K between about 1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³,between about 1×10¹⁶ cm⁻³ and 2×10¹⁹ cm⁻³, below 1×10¹⁷ cm⁻³, below1×10¹⁶ cm⁻³, and below 1×10¹⁶ cm⁻³, respectively, as quantified bycalibrated secondary ion mass spectrometry (SIMS). In anotherembodiment, the top and bottom surfaces of the free-standing, mergedammonothermal group III metal nitride boule or wafer may have impurityconcentrations of O, H, C, and at least one of Na and K between about1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³, between about 1×10¹⁶ cm⁻³ and 2×10¹⁹ cm⁻³,below 1×10¹⁷ cm⁻³, and between about 3×10¹⁵ cm⁻³ and 1×10¹⁸ cm⁻³,respectively, as quantified by calibrated secondary ion massspectrometry (SIMS). In still another embodiment, the top and bottomsurfaces of the free-standing, merged ammonothermal group III metalnitride boule or wafer may have impurity concentrations of O, H, C, andat least one of F and Cl between about 1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³,between about 1×10¹⁶ cm⁻³ and 2×10¹⁹ cm⁻³, below 1×10¹⁷ cm⁻³, andbetween about 1×10¹⁵ cm⁻³ and 1×10¹⁹ cm⁻³, respectively, as quantifiedby calibrated secondary ion mass spectrometry (SIMS). In someembodiments, the top and bottom surfaces of the free-standing, mergedammonothermal group III metal nitride boule or wafer may have impurityconcentrations of H between about 5×10¹⁷ cm⁻³ and 1×10¹⁹ cm⁻³, asquantified by calibrated secondary ion mass spectrometry (SIMS). Incertain embodiments, at least one surface of the free-standing, mergedammonothermal group III metal nitride boule or wafer has an impurityconcentration of copper (Cu), manganese (Mn), and iron (Fe) betweenabout 1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³. In a specific embodiment, thefree-standing, merged ammonothermal group III metal nitride boule orwafer has an infrared absorption peak at about 3175 cm⁻¹, with anabsorbance per unit thickness of greater than about 0.01 cm⁻¹.

The free-standing, merged ammonothermal group III metal nitride crystalor wafer may be characterized by a wurtzite structure substantially freefrom any cubic entities or other crystal structures, the otherstructures being less than about 0.1% in volume in reference to thesubstantially wurtzite structure.

Surprisingly, given the lattice mismatch between HVPE GaN andammonothermal GaN, results of use of the herein-disclosed techniquesshow that ammonothermal lateral epitaxial overgrowth is capable ofproducing thick, large-area GaN layers that are free of cracks. Incertain embodiments, the free-standing, merged ammonothermal group IIImetal nitride crystal or wafer has a diameter larger than about 25millimeters, larger than about 50 millimeters, larger than about 75millimeters, larger than about 100 millimeters, larger than about 150millimeters, larger than about 200 millimeters, larger than about 300millimeters, or larger than about 600 millimeters, and a thicknessgreater than about 0.1 millimeter, greater than about 0.2 millimeter,greater than about 0.3 millimeter, greater than about 0.5 millimeter,greater than about 1 millimeter, greater than about 2 millimeters,greater than about 3 millimeters, greater than about 5 millimeters,greater than about 10 millimeters, or greater than about 20 millimeters,and is substantially free of cracks. By contrast, we find thatammonothermal growth on large-area, un-patterned HVPE GaN seed crystalsleads to cracking if the layers are thicker than a few hundred microns,even if a patterning process had been used to form the HVPE GaN seedcrystal.

A free-standing, merged ammonothermal group III metal nitride wafer maybe characterized by a total thickness variation (TTV) of less than about25 micrometers, less than about 10 micrometers, less than about 5micrometers, less than about 2 micrometers, or less than about 1micrometer, and by a macroscopic bow that is less than about 200micrometers, less than about 100 micrometers, less than about 50micrometers, less than about 25 micrometers, or less than about 10micrometers. A large-area surface of the free-standing, mergedammonothermal group III metal nitride wafer may have a concentration ofmacro defects, with a diameter or characteristic dimension greater thanabout 100 micrometers, of less than about 2 cm⁻², less than about 1cm⁻², less than about 0.5 cm⁻², less than about 0.25 cm⁻², or less thanabout 0.1 cm⁻². The variation in miscut angle across a large-areasurface of the free-standing ammonothermal group III metal nitridecrystal or wafer may be less than about 1 degree, less than about 0.5degree, less than about 0.2 degree, less than about 0.1 degree, lessthan about 0.05 degree, or less than about 0.025 degree in each of twoorthogonal crystallographic directions. The root-mean-square surfaceroughness of a large-area surface of the free-standing, mergedammonothermal group III metal nitride wafer, as measured over an area ofat least 10 μm×10 μm, may be less than about 0.5 nanometer, less thanabout 0.2 nanometer, less than about 0.15 nanometer, less than about 0.1nanometer, or less than about 0.10 nanometer. The free-standing, mergedammonothermal group III metal nitride wafer may be characterized byn-type electrical conductivity, with a carrier concentration betweenabout 1×10¹⁷ cm⁻³ and about 3×10¹⁹ cm⁻³ and a carrier mobility greaterthan about 100 cm²/V-s. In alternative embodiments, the free-standing,merged ammonothermal group III metal nitride wafer is characterized byp-type electrical conductivity, with a carrier concentration betweenabout 1×10¹⁵ cm⁻³ and about 1×10¹⁹ cm⁻³. In still other embodiments, thefree-standing, merged ammonothermal group III metal nitride wafer ischaracterized by semi-insulating electrical behavior, with aroom-temperature resistivity greater than about 10⁷ ohm-centimeter,greater than about 10⁸ ohm-centimeter, greater than about 10⁹ohm-centimeter, greater than about 10¹⁰ ohm-centimeter, or greater thanabout 10¹¹ ohm-centimeter. In certain embodiments, the free-standing,merged ammonothermal group III metal nitride wafer is highlytransparent, with an optical absorption coefficient at a wavelength of400 nanometers that is less than about 10 cm⁻¹, less than about 5 cm⁻¹,less than about 2 cm⁻¹, less than about 1 cm⁻¹, less than about 0.5cm⁻¹. less than about 0.2 cm⁻¹, or less than about 0.1 cm⁻¹.

In some embodiments, the free-standing, merged ammonothermal group IIImetal nitride crystal or wafer is used as a seed crystal for furtherbulk growth. In one specific embodiment, the further bulk growthcomprises, merged ammonothermal bulk crystal growth. In another specificembodiment, the further bulk growth comprises high temperature solutioncrystal growth, also known as flux crystal growth. In yet anotherspecific embodiment, the further bulk growth comprises HVPE. Thefurther-grown crystal may be sliced, lapped, polished, etched, and/orchemically-mechanically polished into wafers by methods that are knownin the art. The surface of the wafers may be characterized by aroot-mean-square surface roughness measured over a 10-micrometer by10-micrometer area that is less than about 1 nanometer or less thanabout 0.2 nanometers.

A wafer may be incorporated into a semiconductor structure. Thesemiconductor structure may comprise at least oneAl_(x)In_(y)Ga_((1-x-y))N epitaxial layer, where 0≤x, y, x+y≤1. Theepitaxial layer may be deposited on the wafer, for example, bymetalorganic chemical vapor deposition (MOCVD) or by molecular beamepitaxy (MBE), according to methods that are known in the art. At leasta portion of the semiconductor structure may form a portion of agallium-nitride-based electronic device or optoelectronic device, suchas a light emitting diode, a laser diode, a power-conversion photodiode,a photodetector, an avalanche photodiode, a photovoltaic, a solar cell,a cell for photoelectrochemical splitting of water, a transistor, arectifier, and a thyristor; one of a transistor, a rectifier, a Schottkyrectifier, a thyristor, a p-i-n diode, a metal-semiconductor-metaldiode, high-electron mobility transistor, a metal semiconductor fieldeffect transistor, a metal oxide field effect transistor, a power metaloxide semiconductor field effect transistor, a power metal insulatorsemiconductor field effect transistor, a bipolar junction transistor, ametal insulator field effect transistor, a heterojunction bipolartransistor, a power insulated gate bipolar transistor, a power verticaljunction field effect transistor, a cascode switch, an inner sub-bandemitter, a quantum well infrared photodetector, a quantum dot infraredphotodetector, and combinations thereof. The gallium-nitride-basedelectronic device or optoelectronic device may be incorporated into alamp or a fixture, such as a luminaire. The gallium-nitride-basedelectronic device or optoelectronic device, after singulation, may havelateral dimensions of at least 0.1 millimeter by 0.1 millimeter. Thegallium-nitride-based electronic or optoelectronic device may have amaximum dimension of at least 8 millimeters and, for example, maycomprise a laser diode. The gallium-nitride-based electronic oroptoelectronic device may be entirely free of dislocations throughoutits volume. For example, at a dislocation density of 10⁴ cm⁻², asubstantial fraction of 0.1×0.1 mm² devices could be expected to be freeof dislocations. At a dislocation density of 10² cm⁻², a substantialfraction of 1×1 mm² devices could be expected to be free ofdislocations. The gallium-nitride-based electronic or optoelectronicdevice may be entirely free of stacking faults throughout its volume.For example, at a stacking fault density of 1 cm⁻¹, a substantialfraction of 10×1 mm² stripe-shaped devices, such as laser diodes withnonpolar or semipolar large area surfaces and c-plane facets, could beexpected to be free of stacking faults.

FIGS. 7A-7D are cross-sectional diagrams illustrating methods andresulting opto-electronic and electronic devices according toembodiments of the present disclosure. A two- or three-terminal device,such as an opto-electronic or electronic device, may be formed by asequence of steps, including the step of epitaxial layer deposition on afree-standing, merged ammonothermal group III metal nitride wafer 431 orsubstrate having a pattern of locally-approximately-linear arrays 419 ofthreading dislocations and comprising at least one AlInGaN active layeror GaN drift layer 631, e.g., by MOCVD, as shown in FIG. 7B. In certainembodiments, the deposited layers include an n-type or n+ layer 633, adoped or unintentionally doped single quantum well (SQW), a multiplequantum well (MQW) structure, a double-heterostructure (DH structure),or an n-drift layer, and a p-type layer 636, as shown. The devicestructures may be vertical, as illustrated schematically in FIGS. 7B and7D, or lateral, as illustrated schematically in FIG. 7C. The device maybe electrically connected to an external circuit to provide a potentialbetween an n-type contact 639 and a p-type contact 637. Additionallayers may be deposited, such as separate confinement heterostructure(SCH) layers, cladding layers, an AlGaN electron-blocking layer, and ap+ contact layer, among others. In many cases, threading dislocations inthe substrates, such as pattern of locally-approximately-linear arrays419, will propagate into the deposited layers and potentially impactdevice performance.

In a specific embodiment, the method also deposits an n-type contact639, and a p-type contact 637 as shown in FIGS. 7B and 7C. In someembodiments, at least one of the set of n-type and p-type contacts isplaced in specific registry respect to the coalescence fronts, wingregions, and/or window regions. A light emission portion may be centeredover the coalescence front, or between coalescence fronts. In onespecific embodiment, transparent p-type contacts are deposited and areplaced in such a way that they avoid contact with coalescence fronts,which may have an elevated concentration of threading dislocations. Inthis way a light-emitting structure or photodiode structure may beformed has a relatively low concentration of threading dislocations. Inthis way a light-emitting structure, PN diode, photodiode, or Schottkybarrier diode may be formed has a relatively low concentration ofthreading dislocations. In preferred embodiments, regions of lightemission and/or maximum electric fields are designed to overlie wingregions 417 and to avoid the pattern of locally-approximately-lineararrays 419. In certain embodiments, a defective region associated with acoalescence front or a window region is utilized as a shunt path forreducing series resistance. In certain embodiments, n-type contacts areplaced above coalescence fronts or window regions, with an edgedislocation density above 10³ cm⁻¹ and/or a threading dislocationdensity greater than about 10⁵ cm⁻².

Referring now to FIG. 7C, in some embodiments, e.g., a laser diode, a PNdiode, a photodiode, or a Schottky barrier diode, the p-contact may beplaced in a region substantially free of coalescence fronts. In certainembodiments, such as a laser diode, a laser ridge or stripe structure740 may be placed in a region substantially free of coalescence fronts.A mesa may be formed by conventional lithography and an n-type contactplaced in electrical contact with the n-type layer and/or the substrate.Additional structures may be placed in registry with the coalescencefronts, such as sidewall passivation, an ion implanted region, fieldplates, and the like.

Referring now to FIG. 7D, in some embodiments, for example, a currentaperture vertical electron transistor (CAVET), an n-drift layer 731 isdeposited over an n+ contact layer 730, which in turn is deposited onfree-standing, merged ammonothermal group III metal nitride wafer 431.P-type layer 735 is formed above n-layer 731 with aperture 736.Following regrowth of the balance of n-layer 731, an AlGaN 2D electrongas layer 738 is deposited. Finally, source contacts 737, drain contact739, dielectric layer 741, and gate contact 743 are deposited. Inpreferred embodiments, aperture 736 is positioned away from firstcoalescence fronts 419 and second coalescence fronts 435. In preferredembodiments, aperture 736 is positioned away from window regions 415. Inpreferred embodiments, aperture 736 is positioned over wing regions 417.Other types of three-terminal devices, such as trench CAVETs, MOSFETs,and the like are positioned so that the regions of maximum electricfields are located within wing regions 417.

FIG. 8 shows a top view (plan view) of a free-standing GaN substrateformed by ammonothermal lateral epitaxial growth using a mask in theform of a two-dimensional array. The GaN layer grew through thetwo-dimensional array of openings in the original mask layer to formwindow regions 415. Coalescence of the GaN layer may form atwo-dimensional grid of the pattern of locally-approximately-lineararrays 419 of threading dislocations.

FIG. 9A shows a top view of a device structure, for example, of LEDs900, where transparent p-contacts 970 have been aligned with respect andplaced so as not to be in contact with either the window regions 415 orthe pattern of locally-approximately-linear arrays 419 of threadingdislocations. FIG. 9B shows a top view of an alternative embodiment of adevice structure, for example, of LEDs 902, where electrical contacts980 are again aligned with respect to window regions 415 and pattern oflocally-approximately-linear arrays 419 of threading dislocations butnow are positioned above pattern of locally-approximately-linear arrays419 of threading dislocations. FIG. 9C shows a top view of analternative embodiment of a device structure 904, for example, of aflip-chip LED, where n-type electrical contacts 990 are aligned withrespect to window regions 415 and p-type electrical contacts 995 arealigned between window regions 415.

Individual die, for example, light emitting diodes or laser diodes, maybe formed by sawing, cleaving, slicing, singulating, or the like,between adjacent sets of electrical contacts. Referring again to FIG.9A, slicing may be performed along the pattern oflocally-approximately-linear arrays 419 of threading dislocations.Slicing may also be performed through window regions 415. Referring nowto FIG. 9B, in certain embodiments, slicing may be performed throughwindow regions 415 but not along the pattern oflocally-approximately-linear arrays 419 of threading dislocations.Referring again to FIG. 9C, in certain embodiments slicing is performedneither through the seed regions nor along all coalescence fronts.Depending on the arrangement of the one- or two-dimensional array ofseed regions, the singulated die may have three corners, four corners,or six corners.

The methods described herein provide means for fabricating large-areagroup III metal nitride substrates, albeit having some potentiallydefective regions. The methods described herein provide means forfabricating high-performance light emitting diodes and/or laser diodesthat avoid potential issues associated with defective regions in thelarge-area group III metal nitride substrates.

Tiled Crystal Array Substrate Example(s)

Referring again to FIG. 19D and also to FIG. 19G, in certainembodiments, rather than using tiled composite structure 1960 as a seedcrystal for further bulk crystal growth, tiled composite structure 1960is processed further to form tiled composite substrate 1980 and useddirectly as a substrate for optical or electronic device fabrication.The formed tiled composite substrate 1980, includes an array of seedcrystals 370 that are bonded together by a polycrystalline GaN layer1950, which may also be referred to as a matrix member. In someembodiments, the array of seed crystals 370 are positioned such that asurface 1975 of each seed crystal is parallel to a first plane, such asthe X-Y plane shown in FIG. 19G. The array of seed crystals 370 may bepositioned such that a gap 1986 (FIG. 19G) is formed between adjacentedges of the seed crystals 370. In one example, the gap 1986 is lessthan 2 millimeters (mm), such as between 0.1 micrometer (μm) and 1millimeters (mm), or between 0.1 micrometer and 200 micrometers, between0.1 micrometer and 50 micrometers, or between 0.2 micrometer and 50micrometers. In certain embodiments, gaps 1986 are completely filledwith matrix member material 1950. In certain embodiments, the topsurface of matrix member material 1950 lies below that of seed crystalsurfaces 1975, as illustrated in FIG. 19D. In certain embodiments, nomatrix member material 1950 is present within gaps 1986, so that seedcrystals 370 are held in place only by a bond from their back sides tomatrix member 1950. In certain embodiments, the surfaces 1975 of seedcrystals 370 within the array are planarized by grinding, lapping,polishing, or the like. In certain embodiments, surfaces 1975 arechemically-mechanically-polished and subjected to a final-cleanoperation in a clean room environment. In certain embodiments, during aprocess used to form the tiled composite substrate 1980 the backside ofa tiled composite structure 1960 is thinned and planarized, for example,by grinding, lapping, and/or polishing. In certain embodiments, thethickness of tiled composite substrate 1980 is the same as the thicknessof seed crystals 370, so that matrix member 1950 is present only withingaps 1986. In other embodiments, the thickness of tiled compositesubstrate 1980 is greater than the thickness of seed crystals 370, inwhich case matrix member 1950 is bonded to the back sides of seedcrystals 370. The perimeter of tiled composite structure 1960 may beground to form outer edge 1990 of tiled composite substrate 1980. Incertain embodiments, a chamfer, bevel, or rounded edge is ground intoedge 1990 of tiled composite substrate 1980. In some embodiments, theouter edge 1990, which surrounds the array of seed crystals 370, iscircular is shape. In certain embodiments, one or more orientation flats1995 may be ground into the edge 1990 of tiled composite substrate 1980.In certain embodiments, tiled composite substrate 1980 has a diameterbetween 20 millimeters and 210 millimeters, between 20 millimeters and30 millimeters, between 45 millimeters and 55 millimeters, between 90millimeters and 110 millimeters, between 140 millimeters and 160millimeters, or between 190 millimeters and 210 millimeters and athickness between 150 micrometers and about 5 millimeters, between about200 micrometers and about 2 millimeters, or between about 250micrometers and about 1.5 millimeters.

In certain embodiments, the thicknesses of each of seed crystals 370within tiled composite substrate 1980 are equal, to within 50micrometers, to within 25 micrometers, to within 10 micrometers, towithin 5 micrometers, to within 2 micrometers, or to within 1micrometer. In certain embodiments, the surfaces 1975 of each of seedcrystals 370 are co-planar, to within 10 micrometers, to within 5micrometers, to within 2 micrometers, or to within 1 micrometer. Thecrystallographic miscut of each of the surfaces 1975 of seed crystals370 have magnitudes that may be equal, within 0.5 degree, within 0.3degree, within 0.2 degree, within 0.1 degree, within 0.05 degree, within0.02 degree, or within 0.01 degree. In preferred embodiments, thedirections of the crystallographic miscuts of each of the seed crystals370 are aligned to within 10 degrees, within 5 degrees, within 2degrees, within 1 degree, within 0.5 degree, within 0.2 degree, orwithin 0.1 degree. In a specific embodiment, each of surfaces 1975 ofseed crystals 370 have an orientation that is within 5 degrees, within 2degrees, within 1 degree, or within 0.5 degree of an orientationselected from {20-2 ±1}, {30-3 ±1}, and {10-10} and a miscut in thea-direction that is less than 0.5 degree, less than 0.2 degree, lessthan 0.1 degree, or less than 0.05 degree.

Tiled composite substrate 1980 may be characterized by a total thicknessvariation (TTV) of less than about 25 micrometers, less than about 10micrometers, less than about 5 micrometers, less than about 2micrometers, or less than about 1 micrometer, and by a macroscopic bowthat is less than about 200 micrometers, less than about 100micrometers, less than about 50 micrometers, less than about 25micrometers, or less than about 10 micrometers. Small values of the TTVand of the macroscopic bow are useful for electronic device fabrication,as they enable deposition of epitaxial layers with uniform propertiesand high device yields. At least one surface 1975 (FIG. 19D) of thetiled composite substrate 1980 may have a concentration of macrodefects, with a diameter or characteristic dimension greater than about100 micrometers, of less than about 2 cm⁻², less than about 1 cm⁻², lessthan about 0.5 cm⁻², less than about 0.25 cm⁻², or less than about 0.1cm⁻². The variation in miscut angle across the ensemble of surfaces 1975of seed crystals 370 may be less than about 1 degree, less than about0.5 degree, less than about 0.2 degree, less than about 0.1 degree, lessthan about 0.05 degree, or less than about 0.025 degree in each of twoorthogonal crystallographic directions. The average root-mean-squaresurface roughness of least one surface 1975 of tiled composite substrate1980, as measured over an area of at least 10 μm×10 μm, may be less thanabout 0.5 nanometer, less than about 0.2 nanometer, less than about 0.15nanometer, less than about 0.1 nanometer, or less than about 0.10nanometer. At least one seed crystal 370 in tiled composite substrate1980 may be characterized by n-type electrical conductivity, with acarrier concentration between about 1×10¹⁷ cm⁻³ and about 3×10¹⁹ cm⁻³and a carrier mobility greater than about 100 cm²N-s. In alternativeembodiments, at least one seed crystal 370 in tiled composite substrate1980 is characterized by p-type electrical conductivity, with a carrierconcentration between about 1×10¹⁵ cm⁻³ and about 1×10¹⁹ cm⁻³. In stillother embodiments, at least one seed crystal 370 in tiled compositesubstrate 1980 wafer is characterized by semi-insulating electricalbehavior, with a room-temperature resistivity greater than about 10⁷ohm-centimeter, greater than about 10⁸ ohm-centimeter, greater thanabout 10⁹ ohm-centimeter, greater than about 10¹⁰ ohm-centimeter, orgreater than about 10¹¹ ohm-centimeter.

One or more device structures may be grown or deposited on one or moreof seed crystals 370 within tiled composite substrate 1980, as shownschematically in FIG. 23A. In certain embodiments, following depositionof first layer 2310, for example, by MOCVD, MBE, or HVPE, a releaselayer 2320 may be deposited thereon. In some embodiments, the firstlayer 2310 may include a layer that is doped with an n-type dopant. Therelease layer 2320 can include or consist of InGaN. The release layer2320 may include or consist of a multiple quantum well or astrained-layer superlattice.

In certain embodiments, device layers 2340 are then deposited, overlyingrelease layer 2320. Device layers 2340 may include one or more of alow-n GaN drift layer, one or more AlInGaN active layers, one or moreAlInGaN cladding layers, a p-type layer, and a p-type electricalcontact. Other layers may also be present in device layers 2340, as maybe suitable for fabrication of devices such as light emitting diodes,laser diodes, photodiodes, diodes, transistors, or the like. In certainembodiments, adhesion layer 2350 may be deposited overlying devicelayers 2340. In some embodiments, trenches 2355 are formed throughadhesion layer 2350, device layers 2340, and into or through releaselayer 2320. As shown schematically in FIG. 23B, the handle substrate2360 is then bonded to the adhesion layer 2350. The process of bondingof handle substrate 2360 to adhesion layer 2350 can be accomplished byone or more of thermocompression bonding, soldering, sinterless silverbonding, or adhesive bonding. In some embodiments, release layer 2320 isthen removed, causing separation of one or more device layers 2340,bonded to handle substrate 2360, from one or more seed crystals 370, asshown schematically in FIG. 23C. In certain embodiments, release layer2320 is removed by photoelectrochemical etching. In certain embodiments,the order of these operations is changed. In one specific embodiment,some or all of release layer 2320 is removed prior to bonding of handlesubstrate 2360 to adhesion layer 2350.

In certain embodiments, surfaces 2370 of seed crystals 370, which mayalso have portions of first layer 2310 or other layers present, may bere-planarized by one or more of grinding, lapping, and polishing. Thesurfaces 2370 may be further prepared by chemical-mechanical polishingand final cleaning in a clean room environment. After removal of devicelayers 2340 from tiled composite substrate 1980 and re-preparation ofsurfaces 2370 of seed crystals 370 within tiled composite substrate1980, tiled composite substrate is again used directly as a substratefor optical or electronic device fabrication. The tiled compositesubstrate 1980 can be re-used at least once, at least twice, at leastthree times, at least five times, or at least ten times as a substrateused in the formation of an optical or electronic device. While FIGS.19A-19E and FIGS. 23A-23C illustrate a configuration in which thepolycrystalline GaN layer 1950 of the tiled composite substrate 1980extends over a surface of the seed crystals 370 (e.g., lower surface inFIGS. 23A-23C) this configuration is not intended to be limiting as toscope of the disclosure herein, since in some configurations thepolycrystalline GaN layer 1950 is only positioned between the edges ofthe seed crystals 370 and not over either of the major surfaces (e.g.,upper and lower surfaces in FIGS. 23A-23B) of the seed crystals 370.

The above sequence of steps provides a method according to an embodimentof the present disclosure. In a specific embodiment, the presentdisclosure provides a method and resulting crystalline material providedby a high pressure apparatus having structured support members. Otheralternatives can also be provided where steps are added, one or moresteps are removed, or one or more steps are provided in a differentsequence without departing from the scope of the claims herein.

EXAMPLES

Embodiments provided by the present disclosure are further illustratedby reference to the following examples. It will be apparent to thoseskilled in the art that many modifications, both to materials, andmethods, may be practiced without departing from the scope of thedisclosure.

Example 1

A c-plane oriented bulk GaN crystal grown by HVPE, approximately 0.3millimeters thick, was provided for use as a substrate 101 forpatterning and ammonothermal crystal growth. A 100-nanometer-thick layerof TiW was sputter-deposited as an adhesion layer on the (000-1) N-faceof the substrate, followed by a 780-nanometer-thick inert layercomprising Au. A 6-micrometer-thick Au layer was then electroplated onthe sputtered layer, increasing the thickness of the inert layer (e.g.,blanket mask 116). Using AZ-4300 as a photoresist (e.g., photoresistlayer 103), a pattern comprising linear arrays of 3-micrometer-wide by1-centimeter-long slits (e.g., openings 112), with a pitch diameter of1200 micrometers was defined. A wet-etch process was performed, using acommercial TFA gold etching solution at room temperature, as shownschematically in FIGS. 1M-1P, to obtain a substrate with patterned masklayer 111. The mask pattern comprised domains of m-stripes, with linearopenings oriented approximately 30-40 micrometers wide and parallel to<10-10>. The substrate with patterned mask layer 111 was then placed ina stirred beaker with concentrated H₃PO₄. The beaker was heated toapproximately 280 degrees Celsius over approximately 30 minutes, held atthis temperature for approximately 90 minutes, and cooled. A crosssection of a trench 115 formed by this procedure, having a depth ofapproximately 162 micrometers and a width at the top of approximately105 micrometers, is shown in FIG. 10 . The sidewalls of the trench 115,remarkably, are nearly vertical.

Example 2

A patterned, trenched c-plane-oriented bulk GaN substrate 101 wasprepared by a similar procedure as that described in Example 1. Thepatterned substrate was placed in a silver capsule along with a15%-open-area baffle, polycrystalline GaN nutrient, NH₄F mineralizer,and ammonia, and the capsule was sealed. The ratios of GaN nutrient andNH₄F mineralizer to ammonia were approximately 1.69 and 0.099respectively, by weight. The capsule was placed in an internally-heatedhigh pressure apparatus and heated to temperatures of approximately 666degrees Celsius for the upper, nutrient zone and approximately 681degrees Celsius for the lower, crystal growth zone, maintained at thesetemperatures for approximately 215 hours, and then cooled and removed.Ammonothermal GaN filled in most of the volume in the trenches, grewthrough the linear openings in the patterned mask on the HVPE GaNsubstrate, grew laterally, and coalesced fully, forming an ammonothermalGaN layer approximately 1200 micrometers thick with a smooth topsurface. Two parallel cuts were made in the ammonothermal GaN layer,perpendicular to both the surface and the patterns, resulting in abar-shaped test specimen with m-plane surfaces. One m-plane surface ofthe test specimen was polished and examined by optical microscopy, asshown in FIGS. 11A and 11B. An interface is visible between thesubstrate 101 and laterally-grown group III metal nitride material 221,as illustrated by the dotted line in the expanded view on the right sideof FIG. 11B. Patterned mask layer 111 and void 225 both appear as blackin the images and underlie ammonothermal group III metal nitride layer213.

Example 3

A patterned, trenched c-plane-oriented bulk GaN substrate was preparedby a similar procedure as that described in Examples 1 and 2, and thefinal group III metal nitride layer 213 is shown in FIG. 12B (i.e.,right side figures). A second patterned substrate was prepared by asimilar procedure except that no trenches were prepared below the maskopenings, and the final group III metal nitride layer is shown in FIG.12A (i.e., left side figures). The patterned substrates were placed in asilver capsule along with a 15%-open-area baffle, polycrystalline GaNnutrient, NH₄F mineralizer, and ammonia, and the capsule was sealed. Theratios of GaN nutrient and NH₄F mineralizer to ammonia wereapproximately 2.05 and 0.099 respectively, by weight. The capsule wasplaced in an internally-heated high pressure apparatus and heated totemperatures of approximately 666 degrees Celsius for the upper,nutrient zone and approximately 678 degrees Celsius for the lower,crystal growth zone, maintained at these temperatures for approximately427 hours, and then cooled and removed. Ammonothermal GaN filled in mostof the volume in the trenches of the trenched substrate (FIG. 12B), grewthrough the linear openings in the patterned mask on the HVPE GaNsubstrate, grew laterally, and coalesced fully, forming an ammonothermalGaN layer approximately 2100 micrometers thick with a smooth topsurface. Ammonothermal GaN layer similarly grew through the linearopenings in the patterned mask on the patterned, untrenched HVPE GaNsubstrate (FIG. 12A), grew laterally, and coalesced fully, forming anammonothermal GaN layer approximately 2100 micrometers thick with asmooth top surface. The surface of both ammonothermal GaN layers werelightly etched and were examined by optical microscopy. Differentialinterference contrast (Nomarski) micrographs and transmissionmicrographs of both layers are shown in FIGS. 12A-12B. The average etchpit density, which is believed to accurately represent the threadingdislocation density, of the ammonothermal GaN layer grown on thepatterned substrate without trenches (FIG. 12A), was approximately1.0×10⁵ cm⁻². The average etch pit density of the ammonothermal GaNlayer grown on the patterned, trenched substrate (FIG. 12B), wasapproximately 1.0×10⁴ cm⁻², a full order-of-magnitude improvement.

Example 4

A patterned, trenched c-plane-oriented bulk GaN substrate was preparedby a similar procedure as that described in Examples 1 and 2 but with apitch of 800 micrometers. The patterned, trenched substrate was placedin a silver capsule along with a 15%-open-area baffle, polycrystallineGaN nutrient, NH₄F mineralizer, and ammonia, and the capsule was sealed.The ratios of GaN nutrient and NH₄F mineralizer to ammonia wereapproximately 1.71 and 0.099 respectively, by weight. The capsule wasplaced in an internally-heated high pressure apparatus and heated totemperatures of approximately 668 degrees Celsius for the upper,nutrient zone and approximately 678 degrees Celsius for the lower,crystal growth zone, maintained at these temperatures for approximately485 hours, and then cooled and removed. Ammonothermal GaN filled in mostof the volume in the trenches of the trenched substrate, grew throughthe linear openings in the patterned mask on the HVPE GaN substrate,grew laterally, and coalesced fully, forming an ammonothermal GaN layerapproximately 980 micrometers thick with a smooth top surface. The HVPEGaN substrate was removed by grinding, and the resulting free-standingammonothermal GaN substrate was polished and chemical-mechanicalpolished. The free-standing ammonothermal GaN substrate was thencharacterized by x-ray diffraction, using a PANalytical X'Pert PROdiffractometer using an electron energy of 45 kV with a 40 mA linefocus, a 0.0002 degree step, a 1 sec dwell time, an Ge(220) mirror, aslit height of 1.0 mm and a slit width of 1.0 mm, at nine differentlocations across the substrate. The results of an analysis of the formedGaN substrate are summarized in FIG. 13 . The range of miscut along[1-100] was measured to be 0.078 degrees over the central 80% of thelarge area surface of the crystal, and the range of miscut along [11-20]was measured to be 0.063 degrees over the central 80% of the large areasurface of the crystal. Thus, in some embodiments, a free standingcrystal having a miscut angle that varies by 0.1 degree or less in thecentral 80% of the large area surface of the crystal along a firstdirection and a miscut angle that varies by 0.1 degree or less in thecentral 80% of the large area surface of the crystal along a seconddirection orthogonal to the first direction. By contrast, an identicalmeasurement on a commercial HVPE wafer resulted in a range of miscutalong [1-100] of 0.224 degrees and a range of miscut along [11-20] of0.236 degrees. The full width at half maximum of the rocking-curve forthe (002) reflection was measured as 36 arc seconds, while that of the(201) reflection was measured as 32 arc seconds, as summarized in thetables and graphs shown FIG. 14 . By contrast, identical measurements ona 50 mm diameter, commercial HVPE substrate produced values of 48 and 53arc seconds, respectively, and identical measurements on a 100 mmdiameter, commercial HVPE substrate produced values of 78 and 93 arcseconds, respectively.

Example 5

A c-plane oriented bulk GaN crystal grown by HVPE, approximately 0.3millimeters thick, was provided for use as a substrate for patterningand ammonothermal crystal growth. A 100-nanometer-thick layer of TiW wassputter-deposited as an adhesion layer on the (000-1) N-face of thesubstrate, followed by a 780-nanometer-thick inert layer comprising Au.A 6-micrometer-thick Au layer was then electroplated on the sputteredlayer, increasing the thickness of the inert layer. A pattern was formedon the N-face of the substrate using a frequency-doubled YAG laser withnano-second pulses. The pattern comprised domains of m-trenches, withlinear openings oriented approximately 50-60 micrometers wide andparallel to <10-10>, with a pitch of 1200 micrometers. The patternedsubstrate was then placed in a stirred beaker with concentrated H₃PO₄.The beaker was heated to approximately 280 degrees Celsius overapproximately 30 minutes, held at this temperature for approximately 60minutes, and cooled. A cross section of a trench formed by thisprocedure, having a depth of approximately 200 micrometers and a widthat the top of approximately 80 micrometers, is shown in FIG. 15 . Thesidewalls of the trench, remarkably, are nearly vertical.

Example 6

A patterned, trenched c-plane-oriented bulk GaN substrate was preparedby a similar procedure as that described in Example 5, except that ahigher power was used for the laser so that slots were formed that fullypenetrated the substrate. After etching with concentrated H₃PO₄ atapproximately 280 degrees Celsius for approximately 30 minutes, thewidth of the slots was approximately 115 micrometers. The patternedsubstrates were placed in a silver capsule along with a 15%-open-areabaffle, polycrystalline GaN nutrient, NH₄F mineralizer, and ammonia, andthe capsule was sealed. The ratios of GaN nutrient and NH₄F mineralizerto ammonia were approximately 1.74 and 0.099 respectively, by weight.The capsule was placed in an internally-heated high pressure apparatusand heated to temperatures of approximately 667 degrees Celsius for theupper, nutrient zone and approximately 681 degrees Celsius for thelower, crystal growth zone, maintained at these temperatures forapproximately 500 hours, and then cooled and removed. Ammonothermal GaNfilled in most of the volume in the trenches of the trenched substrate,grew through the linear openings in the patterned mask on the HVPE GaNsubstrate, grew laterally, and coalesced fully, forming an ammonothermalGaN layer approximately 2010 micrometers thick with a smooth topsurface. The surface of the ammonothermal GaN layer was lightly etchedand was examined by optical microscopy. An optical micrograph of thelayer is shown in FIG. 16 . The etch pits in the rectangles A, B, C, D,E, F, and G shown in FIG. 16 were counted, leading to a determinationthat the average etch pit density, which is believed to accuratelyrepresent the threading dislocation density, of the ammonothermal GaNlayer grown on the patterned, laser-trenched substrate, wasapproximately 6.0×10³ cm⁻².

Example 7

Four c-plane-oriented bulk GaN seed crystals were laser-cut from three100 mm diameter bulk GaN wafers such that linear cut edges wereapproximately a-planes, similar to the configuration shown in FIG. 17E.A 100-nanometer-thick layer of TiW was sputter-deposited as an adhesionlayer on the (000-1) N-face of the seed crystals, followed by a2.6-micrometer-thick layer comprising Ag. A pattern was formed on theN-face of the seed crystals using a frequency-doubled YAG laser withnano-second pulses. The pattern comprised domains of m-trenches, withlinear openings oriented parallel to <10-10>, forming a triangularpattern. The four tiles were placed on a flat Mo backing plate within aMo alignment ring such that the linear tile edges and the offcutdirections were aligned. An Ag circular ring gasket and a Mo circularring clamp were placed over the seed crystals and clamped to the backingplate using four Mo bolts, securing the seed crystals, similar to theconfiguration shown in FIG. 18D. Four additional Mo bolts were installedthrough holes in the two larger seed crystals to secure the latter tothe backing plate and reduce tile bow. The assembled fixture had anexposed circular tile area with a diameter of approximately 5.3 inches.The assembled fixture was placed in a silver capsule along with a7%-open-area baffle, polycrystalline GaN nutrient, NH₄F mineralizer, andammonia, and the capsule was sealed. The ratios of GaN nutrient and NH₄Fmineralizer to ammonia were approximately 2.53 and 0.094 respectively,by weight. The capsule was placed in an internally-heated high pressureapparatus and heated to temperatures of approximately 667 degreesCelsius for the upper, nutrient zone and approximately 680 degreesCelsius for the lower, crystal growth zone, maintained at thesetemperatures for approximately 500 hours, and then cooled and removed.Ammonothermal GaN grew through the linear openings in the patterned maskon the seed crystals, grew laterally, and coalesced between patternedtrenches and between seed crystals, forming an ammonothermal GaN layerapproximately 2600 micrometers thick with a circular diameter ofapproximately 5.3 inches and comprising four domains. X-ray diffractionmeasurements performed across tiled interfaces after growth indicatedapproximately 0.2 degree crystallographic misorientation betweenadjacent tiled domains.

Example 8

Four c-plane-oriented bulk GaN seed crystals are laser cut from three100 mm diameter bulk GaN wafers such that linear cut edges areapproximately a-planes, similar to the configuration shown in FIG. 17E.A 200-nanometer-thick layer of AlN is sputtered on the (0001) Ga-face ofthe seed crystals. A Mo susceptor, comprising a backing plate and analignment ring, is sprayed with very fine BN particles suspected in avolatile organic carrier, forming a release layer. The four seedcrystals are placed (000-1) N-face down on the flat Mo susceptor withinthe Mo alignment ring such that the linear tile edges and the offcutdirections are aligned accurately. The susceptor is placed horizontallyin a poly-GaN reactor and a conformal polycrystalline GaN layer with athickness of approximately 1 mm is grown, forming a continuouspolycrystalline GaN handle on the (0001) Ga-faces of the four seedcrystals. After the polycrystalline GaN growth is completed and thereactor cooled, the susceptor is removed from the poly-GaN reactor withthe seed crystals and polycrystalline GaN intact. The seed crystals,embedded in the polycrystalline GaN matrix, are then separated from theMo backing plate by separation at the release layer. A frequency-doubledYAG laser with nano-second pulses trims the edges of the tiled compositestructure, forming a circular tiled composite with a diameter ofapproximately 5.3 inches. The large area exposed polycrystalline GaNhandle and (000-1) N-face surfaces undergo grinding, polishing, andchemical mechanical polishing. A 100-nanometer-thick layer of TiW issputter-deposited as an adhesion layer on the (000-1) N-face of the seedcrystals, followed by a 1.3-micrometer-thick layer comprising Ag.Six-micrometer-thick Au layers are then electroplated on the (000-1)N-face of the seed crystals and the exposed polycrystalline GaN handlesurface. A pattern is formed on the N-face of the tile pieces using afrequency-doubled YAG laser with nano-second pulses. The patterncomprises domains of m-trenches, with linear openings oriented parallelto <10-10>, forming a triangular pattern. The patterned, tiledcomposited structure is then placed in a silver capsule along with a15%-open-area baffle, polycrystalline GaN nutrient, NH₄F mineralizer,and ammonia, and the capsule is sealed. The ratios of GaN nutrient andNH₄F mineralizer to ammonia are approximately 1.74 and 0.099respectively, by weight. The capsule is placed in an internally-heatedhigh pressure apparatus and heated to temperatures of approximately 667degrees Celsius for the upper, nutrient zone and approximately 681degrees Celsius for the lower, crystal growth zone, maintained at thesetemperatures for approximately 500 hours, and then cooled and removed.Ammonothermal GaN grows through the linear openings in the patternedmask on the seed crystals, grows laterally, and coalesces betweenpatterned trenches and between tile pieces, forming an ammonothermal GaNlayer approximately 3000 micrometers thick.

Example 9

A tiled composite structure similar to that described in Example 8 isprepared, except that 38 seed crystals having a (30-3-1) orientation,dimensions of 10 millimeters in a direction parallel to a c-axisprojection by 20 millimeters in an m-direction, and a thickness of 300micrometers, are used. The edges of the seed crystals comprising theperimeter of the array are laser-trimmed to a 95-millimeter-diametercircle prior to placing the seed crystals, (30-3-1) side down, on the Mosusceptor. After deposition of a 1-millimeter thick polycrystalline GaNmatrix on the (30-31) sides of the seed crystals and the susceptor, thetiled composite structure is removed from the susceptor by separation atthe release layer. The perimeter of the tiled composite structure isground to a diameter of 100 millimeters, and a flat parallel to am-plane of the seed crystals is ground on one edge. The back side of thetiled composite structure is then ground, using a 1000-grit grind wheelfollowed by a 4800-grit grind wheel, to form a flat surface that isaccurately parallel to the front surface. The front side of the tiledcomposite structure is then chemical-mechanically polished, removingapproximately 15 micrometers of material, producing a tiled compositesubstrate with a thickness of 600 micrometers that resembles thesubstrate shown in FIG. 19G.

The tiled composite substrate is then placed on a susceptor in acommercial MOCVD reactor. An n-type GaN layer is deposited, followed byan InGaN strained-layer-superlattice release layer, followed by anothern-type GaN layer, followed by an n-type InGaN cladding layer, followedby an undoped InGaN multiple quantum well, followed by a p-type claddinglayer, followed by a p-type layer and a p-contact layer. Trenches arethen formed by conventional lithography, forming mesas approximately1200 micrometers long along a projection of the c-direction in the(30-3-1) surface and 100 micrometers wide along an orthogonal mdirection. Approximately 95% of the release layers are etched away by aphotoelectrochemical process, using a KOH solution and 405 nanometerillumination. A gold-containing adhesion layer is then deposited on thep-contact layers and the mesa structures are transferred by a sequentialprocess to a silicon carbide handle substrate by means of athermocompression bond, followed by fracture of the unremoved releaselayer. After removal of the mesa structures, the surface of the tiledcomposite substrate is re-prepared by chemical-mechanical polishing.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A free-standing group III metal nitride crystal,comprising: a wurtzite crystal structure; at least two domains, each ofthe at least two domains comprising a group III metal selected fromgallium, aluminum, and indium, or combinations thereof, and nitrogen; afirst surface having a maximum dimension greater than 40 millimeters ina first direction, the first surface comprising a domain surface of eachof the at least two domains, wherein the domain surface of each of theat least two domains has a dimension of at least 10 millimeters in thefirst direction; an average concentration of stacking faults below 10³cm⁻¹; and an average concentration of threading dislocations between 10¹cm⁻² and 10⁶ cm⁻², wherein the average concentration of threadingdislocations on the domain surface of each of the at least two domainsvaries periodically by at least a factor of two in the first direction,the period of the variation in the first direction being between 5micrometers and 20 millimeters, the domain surface of each of the atleast two domains comprises a plurality of first regions, each of theplurality of first regions having a locally-approximately-linear arrayof threading dislocations with a concentration between 5 cm⁻¹ and 10⁵cm⁻¹, the domain surface of each of the at least two domains furthercomprises a plurality of second regions, each of the plurality of secondregions being disposed between an adjacent pair of the plurality offirst regions and having a concentration of threading dislocations below10⁵ cm⁻² and a concentration of stacking faults below 10³ cm⁻¹, thedomain surface of each of the at least two domains further comprises aplurality of third regions, each of the plurality of third regions beingdisposed within one of the plurality of second regions or between anadjacent pair of second regions and having a minimum dimension between10 micrometers and 500 micrometers and threading dislocations with aconcentration between 10³ cm⁻² and 10⁸ cm⁻², the free-standing group IIImetal nitride crystal has a crystallographic miscut that varies by 0.5degrees or less along the first direction and by 0.5 degree or lessalong a second direction orthogonal to the first direction over acentral 80% of an area of the first surface of the free-standing groupIII metal nitride crystal, and the at least two domains are separated bya line of dislocations with a linear density between 50 cm⁻¹ and 5×10⁵cm⁻¹, and a polar misorientation angle γ between a first domain and asecond domain is greater than 0.005 degrees and less than 0.3 degreesand misorientation angles α and β are greater than 0.01 degrees and lessthan 1 degree.
 2. The free-standing group III metal nitride crystal ofclaim 1, wherein the free-standing group III metal nitride crystal has asymmetric x-ray rocking curve full width at half maximum less than 50arcsec.
 3. The free-standing group III metal nitride crystal of claim 1,wherein a pitch dimension between adjacent pairs of first regions in thefirst direction is between 200 micrometers and 2 millimeters.
 4. Thefree-standing group III metal nitride crystal of claim 1, wherein thefirst surface has a crystallographic orientation within 5 degrees of a{10-10} m-plane.
 5. The free-standing group III metal nitride crystal ofclaim 1, wherein the first surface has a crystallographic orientationwithin 5 degrees of a (0001) +c-plane or within 5 degrees of a (000-1)−c-plane.
 6. The free-standing group III metal nitride crystal of claim1, wherein the first surface has a crystallographic orientation within 5degrees of a semipolar orientation selected from {6 0 −6 ±1}, {5 0 −5±1}, {4 0 −4 ±1}, {3 0 −3 ±1}, {5 0 −5 ±2}, {7 0 −7 ±3}, {2 0 −2 ±1}, {30 −3 ±2}, {4 0 −4 ±3}, {5 0 −5 ±4}, {1 0 −1 ±1}, {1 0 −1 ±2}, {1 0 −1±3}, {2 1 −3 ±1}, and {3 0 −3 ±4}.
 7. The free-standing group III metalnitride crystal of claim 1, wherein the first surface has impurityconcentrations of: oxygen (O) between 1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³,hydrogen (H) between 1×10¹⁶ cm⁻³ and 2×10¹⁹ cm⁻³, and at least one offluorine (F) and chlorine (Cl) between 1×10¹⁵ cm⁻³ and 1×10¹⁹ cm⁻³. 8.The free-standing group III metal nitride crystal of claim 1, whereinthe first surface has impurity concentrations of: oxygen (O) between1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³, hydrogen (H) between 1×10¹⁶ cm⁻³ and 2×10¹⁹cm⁻³, and at least one of sodium (Na) and potassium (K) between 3×10¹⁵cm⁻³ and 1×10¹⁸ cm⁻³.
 9. The free-standing group III metal nitridecrystal of claim 1, wherein the plurality of first regions are orientedwithin 5 degrees of a crystallographic plane selected from <1 0 −1 0>,<1 1 −2 0>, and [0 0 0 ±1], and a projection of the crystallographicplane on the first surface.
 10. The free-standing group III metalnitride crystal of claim 1, wherein the domain surface of the at leasttwo domains within the free-standing group III metal nitride crystalfurther comprises a pattern comprising a distribution of the pluralityof first regions, the plurality of the second regions, and the pluralityof third regions, wherein the distribution of first, second and thirdregions is selected from a two-dimensional hexagonal, square,rectangular, trapezoidal, triangular, and one-dimensional linear array.11. The free-standing group III metal nitride crystal of claim 1,further comprising a second surface, wherein the second surface isparallel to the first surface; and the free-standing group III metalnitride crystal is characterized by a thickness between the firstsurface and the second surface between 0.1 millimeter and 1 millimeter,by a total thickness variation of less than 10 micrometers, and by amacroscopic bow less than 50 micrometers.
 12. The free-standing groupIII metal nitride crystal of claim 1, wherein the first surface has aratio of impurity concentration of H to an impurity concentration of Othat is between 0.3 and
 100. 13. The free-standing group III metalnitride crystal of claim 1, wherein each of the at least two domains isseparated by a line of dislocations with a linear density between 50cm⁻¹ and 2×10⁵ cm⁻¹ and a polar misorientation angle γ between the firstdomain and the second domain is between 0.005 degrees and 0.2 degree andazimuthal misorientation angles α and β are loss than between 0.01degrees and 0.5 degree.
 14. The free-standing group III metal nitridecrystal of claim 13, wherein the first surface has impurityconcentrations of: oxygen (O) between 1×10¹⁶ cm⁻³ and 1×10¹⁹ cm⁻³,hydrogen (H) between 1×10¹⁶ cm⁻³ and 2×10¹⁹ cm⁻³, and at least one offluorine (F) and chlorine (Cl) between 1×10¹⁵ cm⁻³ and 1×10¹⁹ cm⁻³. 15.The free-standing group III metal nitride crystal of claim 1, whereinthe free-standing group III metal nitride crystal has a crystallographicmiscut that varies by 0.2 degrees or less along the first direction andby 0.2 degree or less along a second direction orthogonal to the firstdirection within the central 80% of the area of the surface of thefree-standing group III metal nitride crystal.
 16. The free-standinggroup III metal nitride crystal of claim 15, wherein the free-standinggroup III metal nitride crystal has a crystallographic miscut thatvaries by 0.1 degrees or less along the first direction and by 0.1degree or less along a second direction orthogonal to the firstdirection within the central 80% of the area of the surface of thefree-standing group III metal nitride crystal.
 17. The free-standinggroup III metal nitride crystal of claim 1, wherein each of theplurality of third regions has threading dislocations with aconcentration between 10³ cm⁻² and 10⁶ cm⁻².
 18. The free-standing groupIII metal nitride crystal of claim 17, wherein each of the plurality ofthird regions has threading dislocations with a concentration between10³ cm⁻² and 10⁵ cm⁻².